Modulation of stem cells using zinc finger proteins

ABSTRACT

Methods and compositions for modifying stem cells using one or more ZFPs are disclosed. Such methods and compositions are useful for facilitating processes such as, for example, dedifferentiating cells, differentiating stem cells into the desired phenotype, propagating stem cells and/or facilitating cloning.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is continuation of U.S. patent application Ser. No.14/270,038, filed May 5, 2014; which is a divisional of U.S. patentapplication Ser. No. 10/490,787, filed May 31, 2006, now U.S. Pat. No.8,735,153, issued May 27, 2014; which is a 371 application ofPCT/US02/30413, filed Sep. 24, 2002 which claims the benefit of thefollowing U.S. provisional patent application Nos. 60/324,619, filedSep. 24, 2001; 60/367,252, filed Mar. 21, 2002, and 60/374,176, filedApr. 17, 2002. The disclosures of all of the aforementioned applicationsare hereby incorporated by reference in their entireties for allpurposes.

BACKGROUND

Stem cells are undifferentiated cells that exist in many tissues ofembryos and adult mammals. Both adult and embryonic stem cells are ableto differentiate into a variety of cell types and, accordingly, may be asource of replacement cells and tissues that are damaged in the courseof disease, infection, or because of congenital abnormalities. (See,e.g., Lovell-Badge Nature 2001, 414:88-91; Donovan et al. Nature 2001,414:92-97). Various types of putative stem cells exist which; when theydifferentiate into mature cells, carry out the unique functions ofparticular tissues, such as the heart, the liver, or the brain.Pluripotent stem cells are thought to have the potential todifferentiate into almost any cell type, while multipotent stem cellsare believed to have the potential to differentiate into many cell types(Robertson, Meth. Cell Biol. 75:173, 1997; and Pedersen, Reprod. Fertil.Dev. 6:543, 1994).

However, certain cell types (such as nerve cells and cardiac cells)differentiate during development and adult organisms do not replacethese cells. It would be of particularly great value in treating a widevariety of diseases to have renewable sources of stem cells that canreliably differentiate into the desired phenotype. By way of example,Parkinson's Disease (PD) is a progressive degenerative disorder thatappears to be associated with the death of dopamergic neurons extendingfrom the substantia nigra of the brain into the neighboring striatum.Attempts to treat PD by transplanting stem cells collected from thedeveloping brains of aborted fetuses have had mixed results. (See, e.g.,Freed et al. (2001) N. Engl. J. Med. 344:710-719). Further, ethicalconsiderations have mitigated against the use of these embryonic orfetal stem cells. Additionally, it has proven difficult to discoverconditions under which embryonic or adult stem cells differentiate intothe desired phenotype.

Furthermore, even in those cell types, such as epithelial cells andhematopoietic cells that are replaced in adult organisms it has been asignificant challenge to readily and inexpensively obtain stem cells insignificant quantities. For example, mammalian hematopoietic cells(e.g., lymphoid, myeloid and erythroid cells) are all believed to begenerated by a single cell type called the hematopoietic “stem cell.”(Civin et al. (1984) J. Immunol. 133:157-165). However, thesehematopoietic stem cells are very rare in adults, accounting forapproximately 0.01% of bone marrow cells and isolation based on cellsurface proteins such as CD34 results in very small yields. Schemes tofractionate human hematopoietic cells into lineage committed andnon-committed progenitors are technically complicated and often do notpermit the recovery of sufficient cells to address multilineagedifferentiation. (see, e.g., Berenson et al., 1991; Terstappen et al.,1991; Brandt et al. (1988) J. Clinical Investigation 82:1017-1027;Landsdorp and Dragowska (1992) J. Exp. Med. 175:1501-1509; Baum et al.(1992) Proc. Natl. Acad. Sci. 89:2804-2808).

Similarly, existing protocols that induce differentiation ex vivo exertlittle control over cell fate, thereby yielding diverse and impure cellpopulations that are inadequate for projects involving ex vivoreconstitution of the immune system. (See, e.g., Clarke et al. Science2000, 288:1660-1663; Bjornson et al. Science 1999, 283:534-537; Galli etal. Nat Neurosci 2000, 3:986-991; Mezey et al. Science 2000,290:1779-1782; Toma et al. Nat Cell Biol 2001, 3:778-784; Weissman etal. Annu Rev Cell Dev Biol 2001, 17:387-403; Anderson et al. Nat Med2001, 7:393-395; Morrison Curr Biol 2001, 11:R7-9; Lagasse et al. NatMed 2000, 6:1229-1234; Krause et al. Cell 2001, 105:369-377). Inaddition, certain existing protocols for stem cell growth anddifferentiation are dependent on the use of feeder cells whichnecessitates the efficient scale-up of cell culture and createsassociated risks including, infection, cell fusion and/or contamination.

Therefore, although embryonic stem cells (ES cells) can be maintained inculture in an undifferentiated state, ex vivo conversion to a desiredcell type is difficult. See, e.g., Clarke et al. Science (2000)288:1660-1663. Similarly, adult stem cells are very difficult to expandin culture. See, e.g., Reya et al. Nature 2001, 414:105-111; Tang et al.Science 2001, 291:868-871.

Thus, there is a clear need to develop methods for identifying,propagating and altering the state (e.g., by differentiation ordedifferentiation) of stem cells to provide a source of cells that aretransplantable to the CNS, PNS, or other tissues in vivo in order toreplace damaged or diseased tissue.

SUMMARY

Described herein are compositions and methods that utilize the specificgene regulatory ability of designed and/or selected zinc finger proteinswith regard to stem cells. In particular, engineered zinc fingerproteins (ZFPs) can be used to dedifferentiate cells to allow continuedproliferation; to direct the fate of stem cells towards a particulardifferentiated state; and/or to dedifferentiate nuclei into an oocyte oregg type phenotype.

Thus, in one aspect, described herein are methods of altering the stateof differentiation in a cell or population of cells, comprising the stepof administering one or more engineered ZFPs to said cell or populationof cells, wherein the ZFPs alter the state of cellular differentiation.In certain embodiments, the alteration comprises dedifferentiating thecell (or population) into a less specialized state while in otherembodiments, the alteration comprises differentiating the cell (orpopulation) into a more specialized state. In still further embodiments,the cell population comprises one or more pluripotent or multipotentstem cells and the altering comprises enhancing proliferation of saidpluripotent or multipotent stem cells. In certain embodiments, the cellis a stem cell and the altering comprises differentiating said stem cellinto a particular selected lineage.

In certain embodiments, a method to dedifferentiate a specialized cellinto a pluripotent or multipotent stem cell phenotype comprisingadministering to the cell an effective amount of one or more ZFPs isprovided. In certain embodiments, a polynucleotide encoding a ZFP isadministered. The ZFP is preferably engineered to specifically modulateexpression of one or more genes involved in dedifferentiation orreprogramming of a somatic cell.

In another aspect, described herein is a method for propagating orexpanding stem cell populations comprising administering to the stemcell population an effective amount of one or more ZFPs thatspecifically target and modulate expression of genes involved in growthin culture. For example, the ZFPs can modulate expression of growthfactors such as epidermal growth factors (EGFs), fibroblast growthfactors (e.g., betaFGF), and the like.

In yet another aspect, described herein is a method for directing a stemcell to a particular differentiated phenotype.

In any of the methods described herein, one or more of the ZFPs modulateexpression of genes involved in growth or differentiation, for example,one or more factors selected from the group consisting of FGF-1, FGF-2,EGF, EGF-like ligands, TGFalpha, IGF-1, TGFbeta, betaFGF, ciliaryneurotrophic factor, retinoic acid receptor, activin, interleukins, theBcl-2 gene product, platelet-derived growth factor (PDGF), nerve growthfactor (NGF), a macrophage inflammatory protein, tumor necrosis factoralpha, OCT 3/4, GATA-4 and HOXB4. In other embodiments, one or more ofthe ZFPs modulate expression of one or more HLA proteins. The modulationof gene expression may comprise repression or activation. Further, inany of the methods described herein the altering can be performed invitro, in vivo or ex vivo.

In any of the methods described herein, one or more of the ZFPs areadministered as polynucleotides encoding the ZFP or as polypeptides.

In another aspect, compositions comprising multipotent/pluripotent stemcells or populations of cells of a selected lineage are provided, forexample compositions produced by any of the methods described herein. Inpreferred embodiments, the compositions are 80%-100% (or any integertherebetween) purified (e.g., 80%-100% of the cells in the compositionare stem cells or cells of a particular lineage), preferably 95%-100%pure.

In yet another aspect, a method for screening an agent which affectsproliferation, differentiation or survival of stem cells is provided,the method comprising administering the agent to any of the compositionsdescribed herein; and determining if said agent has an effect onproliferation, differentiation or survival of said cell population. Incertain embodiments, the determining comprises determining the effectsof said agent on differentiation of said cell population. In any ofthese methods, the agent is selected from the group consisting of smallmolecules, biological agents, peptides or combinations thereof.

In any of the methods or compositions described herein, the cell can bea prokaryotic cell or a eukaryotic cell, for example a plant cell or ananimal cell (e.g., a human cell or a cell from a domestic animal such asa sheep, cow or pig).

These and other embodiments will be readily apparent to one of skill inthe art in view of the teachings herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows levels of OCT4 mRNA in cells transfected with a vectorencoding a fusion between an OCT4-targeted ZFP and the VP16transcriptional activation domain (v-1547), compared to cellstransfected with a vector encoding green fluorescent protein (GFP).

FIG. 2 shows levels of OCT4 mRNA in cells transfected with a vectorencoding a fusion between an OCT4-targeted ZFP and the KOX-1transcriptional repression domain (x-1547), compared to cellstransfected with a vector encoding green fluorescent protein (GFP).

FIG. 3 shows levels of Otx1 mRNA in cells transfected with a vectorencoding a fusion between an OCT4-targeted ZFP and the VP16transcriptional activation domain (v-1547), compared to cellstransfected with a vector encoding green fluorescent protein (GFP).

FIG. 4 shows levels of Otx1 mRNA in cells transfected with a vectorencoding a fusion between an OCT4-targeted ZFP and the KOX-1transcriptional repression domain (x-1547), compared to cellstransfected with a vector encoding green fluorescent protein (GFP).

FIG. 5 shows levels of Hand1 mRNA in cells transfected with a vectorencoding a fusion between an OCT4-targeted ZFP and the KOX-1transcriptional repression domain (x-1547), compared to cellstransfected with a vector encoding green fluorescent protein (GFP).

FIG. 6 shows levels of HOXB4 mRNA in cells transfected with vectorsencoding fusions comprising either a HOXB4-targeted ZFP and the VP16transcriptional activation domain (v-1135) or a HOXB4-targeted ZFP andthe p65 transcriptional activation domain (s-1135), compared to cellstransfected with a vector encoding green fluorescent protein (GFP).HOXB4 levels in mock-transfected cells are also shown.

DETAILED DESCRIPTION

Disclosed herein are compositions and methods, particularly zinc fingerprotein-containing compositions, useful for (1) dedifferentiatingspecialized cells into a stem cell fate; (2) propagating stem cells forlong periods of time in culture; (3) differentiating stem cells into adesired specialized phenotype; (4) increasing cloning efficiency, forexample by reprogramming somatic nuclei; (5) reducing rejection ofallogenic stem cell grafts; and/or (6) parsing the transcriptionregulatory program that unravels during stem cell ontogeny.

Thus, in one aspect, compositions and methods useful for differentiatingstem cells into a desired differentiated state are provided. To date,stem cells have typically been obtained by isolation from heterogeneouscell populations. For example, neural stem cells have been purified fromthe mammalian forebrain (Reynolds and Weiss, Science 255:1707-1710,1992) and these cells may be capable of differentiating into neurons,astrocytes, and oligodendrocytes. See, PCT publications WO 93/01275, WO94/16718, WO 94/10292 and WO 94/09119. Hematopoietic stem cells havealso been purified. See, U.S. Pat. Nos. 5,681,559 and 5,914,108).

Once isolated, attempts have also been made to maintain stem cells invitro, typically by altering the culture conditions. U.S. Pat. Nos.6,265,175 and 5,980,885 describe how neural stem cells can be maintainedin culture by varying culture conditions such as media components (e.g.,serum, bFGF, EGF, amphiregulin, etc.) and vessel characteristics (e.g.,adherency). In other methods, stem cells are selected for in culture byintroducing a nucleic acid construct encoding an antibiotic resistancegene operably linked to a stem-cell specific promoter and thenpreferentially selecting stem cells in the presence of antibiotic. U.S.Pat. No. 6,146,888.

Similarly, differentiation of stem cells into a desired fate isgenerally accomplished by varying the culture environment and/or byvarying the media components. In both cases, the yields are low and theprocedures laborious and expensive. Therefore, using the compositionsand methods described herein, one can readily and inexpensively obtaincells having the desired differentiation capabilities.

Thus, the methods and compositions disclosed herein allow bothdifferentiation and dedifferentiation of cells, by employing acomposition comprising one or more zinc finger proteins and/orassociated proteins. Engineered zinc finger proteins that are capable ofdirecting stem cells into a desired fate, either by affecting the stemcell via intrinsic signals, extrinsic signals or a combination ofintrinsic and extrinsic signals are employed. The ZFPs can be engineeredfor their ability to regulate gene expression, for example by activatingand/or inhibiting genes involved in differentiation. The disclosure alsocontemplates the use of combinations of ZFPs that modulate expression ofone or more genes involved in propagation, development anddifferentiation.

The methods and compositions described herein also allow for increasedease and efficiency in obtaining cell populations having the desiredcharacteristics. For example, the methods and compositions describedherein can be used to cultivate any particular cell line; in celltherapy techniques (e.g., generation of islet-like cells for diabetespatients and neuronal cells for neurodegenerative diseases); in tissueengineering techniques (e.g., tissue repair, transplantation, etc.);detect changes in differentiation states of cells (e.g., DNA mutations,rearrangements, changes in chromatin structure, etc.); and gene therapy.

Thus, it will be apparent to one of skill in the art that ZFP(s) can beused facilitate the regulation of many processes involved in developmentand differentiation, including growth and self-renewal of stem cells;dedifferentiation; differentiation to a desired specialized cell type;and cloning.

Advantages of the presently-disclosed methods and compositions include,but are not limited to, (i) the ability to directly and specificallycontrol core processes that direct stem cell differentiation (e.g.,modulate expression of one or more genes, either by activating orrepressing genes); (ii) the ability to reprogram stem cells ex vivo;(iii) the ability to generate all functional splice variants of thetarget protein; (iv) the ability to limit or eliminate uncontrolledmassive overexpression of a target protein to toxic levels; (v) theability to direct stem cell differentiation or dedifferentiation throughepigenetic mechanisms; (vi) the ability to screen ZFP-TF libraries forZFP-TFs that control differentiation, to identify additional genes thatare important for stem cell differentiation; and (vii) the ability togenerate animal models of ZFP-TF expression and in vivo regulation ofstem cell differentiation.

General

Practice of the disclosed methods and use of the disclosed compositionsemploy, unless otherwise indicated, conventional techniques in molecularbiology, biochemistry, chromatin structure and analysis, computationalchemistry, cell culture, recombinant DNA and related fields as arewithin the skill of the art. These techniques are fully explained in theliterature. See, for example, Sambrook et al. MOLECULAR CLONING: ALABORATORY MANUAL, Second edition, Cold Spring Harbor Laboratory Press,1989; Ausubel et al., CURRENT PROTOCOLS IN MOLECULAR BIOLOGY, John Wiley& Sons, New York, 1987 and periodic updates; the series METHODS INENZYMOLOGY, Academic Press, San Diego; Wolffe, CHROMATIN STRUCTURE ANDFUNCTION, Third edition, Academic Press, San Diego, 1998; METHODS INENZYMOLOGY, Vol. 304, “Chromatin” (P. M. Wassarman and A. P. Wolffe,eds.), Academic Press, San Diego, 1999; and METHODS IN MOLECULARBIOLOGY, Vol. 119, “Chromatin Protocols” (P. B. Becker, ed.) HumanaPress, Totowa, 1999.

All patents, patent applications, and publications mentioned herein,whether supra or infra, are hereby incorporated by reference in theirentirety.

Definitions

The terms “nucleic acid,” “polynucleotide,” and “oligonucleotide” areused interchangeably and refer to a deoxyribonucleotide orribonucleotide polymer in either single- or double-stranded form. Whennot used to refer to a nucleic acid obtained from an organism, the termcan encompass known analogues of natural nucleotides, as well asnucleotides that are modified in the base, sugar, and/or phosphatemoieites.

The terms “totipotent” or “multipotent” refer to a cell in a developingcell mass such as, for example, an embryo or a fetus, that canpotentially give rise to all of the cells in an adult organism. The term“multipotent” refers to a cell that can differentiate into many, but notall of the cell types of an adult organism. Certain stem cellpopulations can be derived from adult organisms while embryonic stemcells are derived from embryonic or fetal tissue. Embryonic stem cellsare derived from a group of cells called the inner cell mass, which partof the blastocyst (4-5 days post fertilization in humans). A review ofthe state of stem cell research was published by NIH in June, 2001 andis available on the world-wide web athttp://www.nih.gov/news/stemcell/scireport.html.

The term “differentiation” refers to process(es) by which previouslyunspecialized cells become specialized for particular functions. Incertain cases, cells may be undergo a stage of commitment ordetermination that precedes the onset of overt differentiation.Typically, cells of a committed or differentiated state express uniquesets of the genes. Similarly, the term “dedifferentiation” refers to areversal of differentiation, in which cells that have been committed andmodified to fulfill a particular specialized function lose theirspecialized character and return to a relatively unspecialized structureand function. The terms are used to refer to any change or alteration incellular differentiation state. Thus, dedifferentiation can refer to anyreversal in differentiated state and does not imply that the cell mustbe reversed to a pluripotent state.

The term “differentiated cell” refers to a cell that has developed froma relatively unspecialized phenotype to a more specialized phenotype.For example, a progenitor cell type such as a hematopoietic stem cellcan give rise to a more differentiated cell such as a monocyte or anerythrocyte. The term “dedifferentiated cell” refers to a cell that hadformerly attained a particular degree of differentiation, but hassubsequently been immortalized or regained the ability to differentiateinto one or more specialized cells (e.g., has become pluripotent ortotipotent). It is highly unlikely that differentiated cells will revertinto their precursor cells (e.g., dedifferentiate) in vivo or in vitro.However, using the method and compositions described herein,differentiated cells can be reprogrammed into immortalized, pluripotentor totipotent cells. Differentiated cells can be isolated from embryonicor somatic cells using techniques known in the art.

The terms “convert,” “reprogram” and “dedifferentiate” are usedinterchangeably to refer to the phenomenon in which a differentiatedcell becomes immortalized, pluripotent and/or totipotent. Cells can bededifferentiated or converted to varying degrees. For example, it ispossible that only a small portion of cells are converted or that anindividual cell is reprogrammed to be pluripotent but not necessarilytotipotent. Thus, the terms “converting,” “reprogramming” or“dedifferentiating” compositions refer to compositions such as, forexample, ZFPs that are able to dedifferentiate a target cell by activelyremodeling chromatin and reversing binding of transcription factors.

A “binding protein” “or binding domain” is a protein or polypeptide thatis able to bind non-covalently to another molecule. A binding proteincan bind to, for example, a DNA molecule (a DNA-binding protein), an RNAmolecule (an RNA-binding protein) and/or a protein molecule (aprotein-binding protein). In the case of a protein-binding protein, itcan bind to itself (to form homodimers, homotrimers, etc.) and/or it canbind to one or more molecules of a different protein or proteins. Abinding protein can have more than one type of binding activity. Forexample, zinc finger proteins have DNA-binding, RNA-binding andprotein-binding activity.

A “zinc finger binding protein” is a protein or polypeptide that bindsDNA, RNA and/or protein, preferably in a sequence-specific manner, as aresult of stabilization of protein structure through coordination of azinc ion. The term zinc finger binding protein is often abbreviated aszinc finger protein or ZFP. The individual DNA binding domains aretypically referred to as “fingers.” A ZFP has least one finger,typically two fingers, three fingers, or six fingers. Each finger bindsfrom two to four base pairs of DNA, typically three or four base pairsof DNA. A ZFP binds to a nucleic acid sequence called a target site ortarget segment. Each finger typically comprises an approximately 30amino acid, zinc-chelating, DNA-binding subdomain. An exemplary motifcharacterizing one class of these proteins (C₂H₂ class) is-Cys-(X)₂₋₄-Cys-(X)₁₂-His-(X)₃₋₅-His (where X is any amino acid).Studies have demonstrated that a single zinc finger of this classconsists of an alpha helix containing the two invariant histidineresidues co-ordinated with zinc along with the two cysteine residues ofa single beta turn (see, e.g., Berg & Shi, Science 271:1081-1085(1996)).

A “designed” zinc finger protein is a protein not occurring in naturewhose structure and composition result principally from rationalcriteria. Rational criteria for design include application ofsubstitution rules and computerized algorithms for processinginformation in a database storing information of existing ZFP designsand binding data, for example as described in co-owned PCT WO 00/42219.A “selected” zinc finger protein is a protein not found in nature whoseproduction results primarily from an empirical process such as phagedisplay. See e.g., U.S. Pat. No. 5,789,538; U.S. Pat. No. 6,007,988;U.S. Pat. No. 6,013,453; WO 95/19431; WO 96/06166 and WO 98/54311. An“engineered” zinc finger protein is a non-naturally occurring ZFP, forexample a ZFP that has been either designed and/or selected.

A “gene,” for the purposes of the present disclosure, includes a DNAregion encoding a gene product (see infra), as well as all DNA regionsthat regulate the production of the gene product, whether or not suchregulatory sequences are adjacent to coding and/or transcribedsequences. Accordingly, a gene includes, but is not necessarily limitedto, promoter sequences, terminators, translational regulatory sequencessuch as ribosome binding sites and internal ribosome entry sites,enhancers, silencers, insulators, boundary elements, replicationorigins, matrix attachment sites and locus control regions.

A “target site” or “target sequence” is a sequence that is bound by abinding protein such as, for example, a ZFP. Target sequences can benucleotide sequences (either DNA or RNA) or amino acid sequences. Asingle target site typically has about four to about ten base pairs.Typically, a two-fingered ZFP recognizes a four to seven base pairtarget site, a three-fingered ZFP recognizes a six to ten base pairtarget site, and a six fingered ZFP recognizes two adjacent nine to tenbase pair target sites. By way of example, a DNA target sequence for athree-finger ZFP is generally either 9 or 10 nucleotides in length,depending upon the presence and/or nature of cross-strand interactionsbetween the ZFP and the target sequence. Target sequences can be foundin any DNA or RNA sequence, including regulatory sequences, exons,introns, or any non-coding sequence.

A “target subsite” or “subsite” is the portion of a DNA target site thatis bound by a single zinc finger, excluding cross-strand interactions.Thus, in the absence of cross-strand interactions, a subsite isgenerally three nucleotides in length. In cases in which a cross-strandinteraction occurs (e.g., a “D-able subsite,” as described for examplein co-owned PCT WO 00/42219, incorporated by reference in its entiretyherein) a subsite is four nucleotides in length and overlaps withanother 3- or 4-nucleotide subsite.

The term “naturally-occurring” is used to describe an object that can befound in nature, as distinct from being artificially produced by ahuman.

An “exogenous molecule” is a molecule that is not normally present in acell, but can be introduced into a cell by one or more genetic,biochemical or other methods. Normal presence in the cell is determinedwith respect to the particular developmental stage and environmentalconditions of the cell. Thus, for example, a molecule that is presentonly during embryonic development of muscle is an exogenous moleculewith respect to an adult muscle cell. Similarly, a molecule induced byheat shock is an exogenous molecule with respect to a non-heat-shockedcell. An exogenous molecule can comprise, for example, a functioningversion of a malfunctioning endogenous molecule or a malfunctioningversion of a normally-functioning endogenous molecule. Thus, the term“exogenous regulatory molecule” refers to a molecule that can modulategene expression in a target cell but which is not encoded by thecellular genome of the target cell.

An exogenous molecule can be, among other things, a small molecule, suchas is generated by a combinatorial chemistry process, or a macromoleculesuch as a protein, nucleic acid, carbohydrate, lipid, glycoprotein,lipoprotien, polysaccharide, any modified derivative of the abovemolecules, or any complex comprising one or more of the above molecules.Nucleic acids include DNA and RNA, can be single- or double-stranded;can be linear, branched or circular; and can be of any length. Nucleicacids include those capable of forming duplexes, as well astriplex-forming nucleic acids. See, for example, U.S. Pat. Nos.5,176,996 and 5,422,251. Proteins include, but are not limited to,DNA-binding proteins, transcription factors, chromatin remodelingfactors, methylated DNA binding proteins, polymerases, methylases,demethylases, acetylases, deacetylases, kinases, phosphatases,integrases, recombinases, ligases, topoisomerases, gyrases andhelicases.

An exogenous molecule can be the same type of molecule as an endogenousmolecule, e.g., protein or nucleic acid (e.g., an exogenous gene),providing it has a sequence that is different from an endogenousmolecule. For example, an exogenous nucleic acid can comprise aninfecting viral genome, a plasmid or episome introduced into a cell, ora chromosome that is not normally present in the cell. Methods for theintroduction of exogenous molecules into cells are known to those ofskill in the art and include, but are not limited to, lipid-mediatedtransfer (e.g., liposomes, including neutral and cationic lipids),electroporation, direct injection, cell fusion, particle bombardment,calcium phosphate co-precipitation, DEAE-dextran-mediated transfer andviral vector-mediated transfer.

By contrast, an “endogenous molecule” is one that is normally present ina particular cell at a particular developmental stage under particularenvironmental conditions. For example, an endogenous nucleic acid cancomprise a chromosome, the genome of a mitochondrion, chloroplast orother organelle, or a naturally-occurring episomal nucleic acid.Additional endogenous molecules can include proteins, for example,transcription factors and components of chromatin remodeling complexes.

Thus, an “endogenous cellular gene” refers to a gene that is native to acell, which is in its normal genomic and chromatin context, and which isnot heterologous to the cell. Such cellular genes include, e.g., animalgenes, plant genes, bacterial genes, protozoal genes, fungal genes,mitrochondrial genes, and chloroplastic genes.

An “endogenous gene” refers to a microbial or viral gene that is part ofa naturally occurring microbial or viral genome in a microbially orvirally infected cell. The microbial or viral genome can beextrachromosomal or integrated into the host chromosome. This term alsoencompasses endogenous cellular genes, as described above.

“Administering” an expression vector, nucleic acid, ZFP, or a deliveryvehicle to a cell comprises transducing, transfecting, electroporating,translocating, fusing, phagocytosing, shooting or ballistic methods,etc., e.g., any means by which a protein or nucleic acid can betransported across a cell membrane and preferably into the nucleus of acell.

The term “effective amount” includes that amount which results in thedesired result, for example, deactivation of a previously activatedgene, activation of a previously repressed gene, or inhibition oftranscription of a structural gene or translation of RNA.

A “delivery vehicle” refers to a compound, e.g., a liposome, toxin, or amembrane translocation polypeptide, which is used to administer a ZFP.Delivery vehicles can also be used to administer nucleic acids encodingZFPs, e.g., a lipid:nucleic acid complex, an expression vector, a virus,and the like.

“Gene expression” refers to the conversion of the information, containedin a gene, into a gene product. A gene product can be the directtranscriptional product of a gene (e.g., mRNA, tRNA, rRNA, antisenseRNA, ribozyme, structural RNA or any other type of RNA) or a proteinproduced by translation of a mRNA. Gene products also include RNAs thatare modified, by processes such as capping, polyadenylation,methylation, and editing, and proteins modified by, for example,methylation, acetylation, phosphorylation, ubiquitination,ADP-ribosylation, myristilation, and glycosylation.

“Gene activation” and “augmentation of gene expression” refer to anyprocess that results in an increase in production of a gene product. Agene product can be either RNA (including, but not limited to, mRNA,rRNA, tRNA, and structural RNA) or protein. Accordingly, gene activationincludes those processes that increase transcription of a gene and/ortranslation of a mRNA. Examples of gene activation processes whichincrease transcription include, but are not limited to, those whichfacilitate formation of a transcription initiation complex, those whichincrease transcription initiation rate, those which increasetranscription elongation rate, those which increase processivity oftranscription and those which relieve transcriptional repression (by,for example, blocking the binding of a transcriptional repressor). Geneactivation can constitute, for example, inhibition of repression as wellas stimulation of expression above an existing level. Examples of geneactivation processes that increase translation include those thatincrease translational initiation, those that increase translationalelongation and those that increase mRNA stability. In general, geneactivation comprises any detectable increase in the production of a geneproduct, preferably an increase in production of a gene product by about2-fold, more preferably from about 2- to about 5-fold or any integertherebetween, more preferably between about 5- and about 10-fold or anyinteger therebetween, more preferably between about 10- and about20-fold or any integer therebetween, still more preferably between about20- and about 50-fold or any integer therebetween, more preferablybetween about 50- and about 100-fold or any integer therebetween, morepreferably 100-fold or more.

“Gene repression” and “inhibition of gene expression” refer to anyprocess that results in a decrease in production of a gene product. Agene product can be either RNA (including, but not limited to, mRNA,rRNA, tRNA, and structural RNA) or protein. Accordingly, gene repressionincludes those processes that decrease transcription of a gene and/ortranslation of a mRNA. Examples of gene repression processes whichdecrease transcription include, but are not limited to, those whichinhibit formation of a transcription initiation complex, those whichdecrease transcription initiation rate, those which decreasetranscription elongation rate, those which decrease processivity oftranscription and those which antagonize transcriptional activation (by,for example, blocking the binding of a transcriptional activator). Generepression can constitute, for example, prevention of activation as wellas inhibition of expression below an existing level. Examples of generepression processes that decrease translation include those thatdecrease translational initiation, those that decrease translationalelongation and those that decrease mRNA stability. Transcriptionalrepression includes both reversible and irreversible inactivation ofgene transcription. In general, gene repression comprises any detectabledecrease in the production of a gene product, preferably a decrease inproduction of a gene product by about 2-fold, more preferably from about2- to about 5-fold or any integer therebetween, more preferably betweenabout 5- and about 10-fold or any integer therebetween, more preferablybetween about 10- and about 20-fold or any integer therebetween, stillmore preferably between about 20- and about 50-fold or any integertherebetween, more preferably between about 50- and about 100-fold orany integer therebetween, more preferably 100-fold or more. Mostpreferably, gene repression results in complete inhibition of geneexpression, such that no gene product is detectable.

“Eucaryotic cells” include, but are not limited to, fungal cells (suchas yeast), plant cells, animal cells, mammalian cells and human cells.

The term “modulate” refers to a change in the quantity, degree or extentof a function. For example, the modified zinc finger-nucleotide bindingpolypeptides disclosed herein may modulate the activity of a promotersequence by binding to a motif within the promoter, thereby inducing,enhancing or suppressing transcription of a gene operatively linked tothe promoter sequence. Alternatively, modulation may include inhibitionof transcription of a gene wherein the modified zinc finger-nucleotidebinding polypeptide binds to the structural gene and blocks DNAdependent RNA polymerase from reading through the gene, thus inhibitingtranscription of the gene. The structural gene may be a normal cellulargene or an oncogene, for example. Alternatively, modulation may includeinhibition of translation of a transcript. Thus, “modulation” of geneexpression includes both gene activation and gene repression.

Modulation of gene expression can be assayed by determining anyparameter that is indirectly or directly affected by the expression ofthe target gene. Such parameters include, e.g., changes in RNA orprotein levels; changes in protein activity; changes in product levels;changes in downstream gene expression; changes in transcription oractivity of reporter genes such as, for example, luciferase, CAT,beta-galactosidase, or GFP (see, e.g., Mistili & Spector, (1997) NatureBiotechnology 15:961-964); changes in signal transduction; changes inphosphorylation and dephosphorylation; changes in receptor-ligandinteractions; changes in concentrations of second messengers such as,for example, cGMP, cAMP, IP₃, and Ca²⁺; changes in cell growth, changesin neovascularization, and/or changes in any functional effect of geneexpression. Measurements can be made in vitro, in vivo, and/or ex vivo.Such functional effects can be measured by conventional methods, e.g.,measurement of RNA or protein levels, measurement of RNA stability,and/or identification of downstream or reporter gene expression. Readoutcan be by way of, for example, chemiluminescence, fluorescence,colorimetric reactions, antibody binding, inducible markers, ligandbinding assays; changes in intracellular second messengers such as cGMPand inositol triphosphate (IP₃); changes in intracellular calciumlevels; cytokine release, and the like.

Accordingly, the terms “modulating expression” “inhibiting expression”and “activating expression” of a gene can refer to the ability of amolecule to activate or inhibit transcription of a gene. Activationincludes prevention of transcriptional inhibition (e.g., prevention ofrepression of gene expression) and inhibition includes prevention oftranscriptional activation (e.g., prevention of gene activation).

To determine the level of gene expression modulation by a ZFP, cellscontacted with ZFPs are compared to control cells, e.g., without thezinc finger protein or with a non-specific ZFP, to examine the extent ofinhibition or activation. Control samples are assigned a relative geneexpression activity value of 100%. Modulation/inhibition of geneexpression is achieved when the gene expression activity value relativeto the control is about 80%, preferably 50% (e.g., 0.5× the activity ofthe control), more preferably 25%, more preferably 5-0%.Modulation/activation of gene expression is achieved when the geneexpression activity value relative to the control is 110%, morepreferably 150% (e.g., 1.5× the activity of the control), morepreferably 200-500%, more preferably 1000-2000% or more.

A “promoter” is defined as an array of nucleic acid control sequencesthat direct transcription. As used herein, a promoter typically includesnecessary nucleic acid sequences near the start site of transcription,such as, in the case of certain RNA polymerase II type promoters, a TATAelement, enhancer, CCAAT box, SP-1 site, etc. As used herein, a promoteralso optionally includes distal enhancer or repressor elements, whichcan be located as much as several thousand base pairs from the startsite of transcription. The promoters often have an element that isresponsive to transactivation by a DNA-binding moiety such as apolypeptide, e.g., a nuclear receptor, Gal4, the lac repressor and thelike.

A “constitutive” promoter is a promoter that is active under mostenvironmental and developmental conditions. An “inducible” promoter is apromoter that is active under certain environmental or developmentalconditions.

A “weak promoter” refers to a promoter having about the same activity asa wild type herpes simplex virus (“HSV”) thymidine kinase (“tk”)promoter or a mutated HSV tk promoter, as described in Eisenberg &McKnight, Mol. Cell. Biol. 5:1940-1947 (1985).

A “transcriptional activator” and a “transcriptional repressor” refer toproteins or functional fragments of proteins that have the ability tomodulate transcription, as described above. Such proteins include, e.g.,transcription factors and co-factors (e.g., KRAB, MAD, ERD, SID, nuclearfactor kappa B subunit p65, early growth response factor 1, and nuclearhormone receptors, VP16, VP64), endonucleases, integrases, recombinases,methyltransferases, histone acetyltransferases, histone deacetylasesetc. Activators and repressors include co-activators and co-repressors(see, e.g., Utley et al., Nature 394:498-502 (1998)).

A “regulatory domain” or “functional domain” refers to a protein or apolypeptide sequence that has transcriptional modulation activity, orthat is capable of interacting with proteins and/or protein domains thathave transcriptional modulation activity. Typically, a functional domainis covalently or non-covalently linked to a DNA-binding domain (e.g., aZFP) to modulate transcription of a gene of interest. Alternatively, aZFP can act, in the absence of a functional domain, to modulatetranscription. Furthermore, transcription of a gene of interest can bemodulated by a ZFP linked to multiple functional domains.

A “functional fragment” of a protein, polypeptide or nucleic acid is aprotein, polypeptide or nucleic acid whose sequence is not identical tothe full-length protein, polypeptide or nucleic acid, yet retains thesame function as the full-length protein, polypeptide or nucleic acid. Afunctional fragment can possess more, fewer, or the same number ofresidues as the corresponding native molecule, and/or can contain oneore more amino acid or nucleotide substitutions. Methods for determiningthe function of a nucleic acid (e.g., coding function, ability tohybridize to another nucleic acid) are well-known in the art. Similarly,methods for determining protein function are well-known. For example,the DNA-binding function of a polypeptide can be determined, forexample, by filter-binding, electrophoretic mobility-shift, orimmunoprecipitation assays. See Ausubel et al., supra. The ability of aprotein to interact with another protein can be determined, for example,by co-immunoprecipitation, two-hybrid assays or complementation, bothgenetic and biochemical. See, for example, Fields et al. (1989) Nature340:245-246; U.S. Pat. No. 5,585,245 and PCT WO 98/44350.

A “fusion molecule” is a molecule in which two or more subunit moleculesare linked, preferably covalently. The subunit molecules can be the samechemical type of molecule, or can be different chemical types ofmolecules. Examples of the first type of fusion molecule include, butare not limited to, fusion polypeptides (for example, a fusion between aZFP DNA-binding domain and a transcriptional activation domain) andfusion nucleic acids (for example, a nucleic acid encoding the fusionpolypeptide described herein). Examples of the second type of fusionmolecule include, but are not limited to, a fusion between atriplex-forming nucleic acid and a polypeptide, and a fusion between aminor groove binder and a nucleic acid.

The term “heterologous” is a relative term, which when used withreference to portions of a nucleic acid indicates that the nucleic acidcomprises two or more subsequences that are not found in the samerelationship to each other in nature. For instance, a nucleic acid thatis recombinantly produced typically has two or more sequences fromunrelated genes synthetically arranged to make a new functional nucleicacid, e.g., a promoter from one source and a coding region from anothersource. The two nucleic acids are thus heterologous to each other inthis context. When added to a cell, the recombinant nucleic acids wouldalso be heterologous to the endogenous genes of the cell. Thus, in achromosome, a heterologous nucleic acid would include an non-native(non-naturally occurring) nucleic acid that has integrated into thechromosome, or a non-native (non-naturally occurring) extrachromosomalnucleic acid. In contrast, a naturally translocated piece of chromosomewould not be considered heterologous in the context of this patentapplication, as it comprises an endogenous nucleic acid sequence that isnative to the mutated cell.

Similarly, a heterologous protein indicates that the protein comprisestwo or more subsequences that are not found in the same relationship toeach other in nature (e.g., a “fusion protein,” where the twosubsequences are encoded by a single nucleic acid sequence). See, e.g.,Ausubel, supra, for an introduction to recombinant techniques.

The term “recombinant” when used with reference, e.g., to a cell, ornucleic acid, protein, or vector, indicates that the cell, nucleic acid,protein or vector, has been modified by the introduction of aheterologous nucleic acid or protein or the alteration of a nativenucleic acid or protein, or that the cell is derived from a cell somodified. Thus, for example, recombinant cells express genes that arenot found within the native (naturally occurring) form of the cell orexpress a second copy of a native gene that is otherwise normally orabnormally expressed, under expressed or not expressed at all.

The terms “operative linkage” and “operatively linked” are used withreference to a juxtaposition of two or more components (such as sequenceelements), in which the components are arranged such that bothcomponents function normally and allow the possibility that at least oneof the components can mediate a function that is exerted upon at leastone of the other components. By way of illustration, a transcriptionalregulatory sequence, such as a promoter, is operatively linked to acoding sequence if the transcriptional regulatory sequence controls thelevel of transcription of the coding sequence in response to thepresence or absence of one or more transcriptional regulatory factors.An operatively linked transcriptional regulatory sequence is generallyjoined in cis with a coding sequence, but need not be directly adjacentto it. For example, an enhancer can constitute a transcriptionalregulatory sequence that is operatively-linked to a coding sequence,even though they are not contiguous.

With respect to fusion polypeptides, the term “operatively linked” canrefer to the fact that each of the components performs the same functionin linkage to the other component as it would if it were not so linked.For example, with respect to a fusion polypeptide in which a ZFPDNA-binding domain is fused to a transcriptional activation domain (orfunctional fragment thereof), the ZFP DNA-binding domain and thetranscriptional activation domain (or functional fragment thereof) arein operative linkage if, in the fusion polypeptide, the ZFP DNA-bindingdomain portion is able to bind its target site and/or its binding site,while the transcriptional activation domain (or functional fragmentthereof) is able to activate transcription.

A “functional fragment” of a protein, polypeptide or nucleic acid is aprotein, polypeptide or nucleic acid whose sequence is not identical tothe full-length protein, polypeptide or nucleic acid, yet retains thesame function as the full-length protein, polypeptide or nucleic acid. Afunctional fragment can possess more, fewer, or the same number ofresidues as the corresponding native molecule, and/or can contain oneore more amino acid or nucleotide substitutions. Methods for determiningthe function of a nucleic acid (e.g., coding function, ability tohybridize to another nucleic acid) are well-known in the art. Similarly,methods for determining protein function are well-known. For example,the DNA-binding function of a polypeptide can be determined, forexample, by filter-binding, electrophoretic mobility-shift, orimmunoprecipitation assays. See Ausubel et al., supra. The ability of aprotein to interact with another protein can be determined, for example,by co-immunoprecipitation, two-hybrid assays or complementation, bothgenetic and biochemical. See, for example, Fields et al. (1989) Nature340:245-246; U.S. Pat. No. 5,585,245 and PCT WO 98/44350.

The term “recombinant,” when used with reference to a cell, indicatesthat the cell replicates an exogenous nucleic acid, or expresses apeptide or protein encoded by an exogenous nucleic acid. Recombinantcells can contain genes that are not found within the native(non-recombinant) form of the cell. Recombinant cells can also containgenes found in the native form of the cell wherein the genes aremodified and re-introduced into the cell by artificial means. The termalso encompasses cells that contain a nucleic acid endogenous to thecell that has been modified without removing the nucleic acid from thecell; such modifications include those obtained by gene replacement,site-specific mutation, and related techniques.

A “recombinant expression cassette” or simply an “expression cassette”is a nucleic acid construct, generated recombinantly or synthetically,that has control elements that are capable of effecting expression of astructural gene that is operatively linked to the control elements inhosts compatible with such sequences. Expression cassettes include atleast promoters and optionally, transcription termination signals.Typically, the recombinant expression cassette includes at least anucleic acid to be transcribed (e.g., a nucleic acid encoding a desiredpolypeptide) and a promoter. Additional factors necessary or helpful ineffecting expression can also be used as described herein. For example,an expression cassette can also include nucleotide sequences that encodea signal sequence that directs secretion of an expressed protein fromthe host cell. Transcription termination signals, enhancers, and othernucleic acid sequences that influence gene expression can also beincluded in an expression cassette.

The term “naturally occurring,” as applied to an object, means that theobject can be found in nature.

The terms “polypeptide,” “peptide” and “protein” are usedinterchangeably to refer to a polymer of amino acid residues. The termalso applies to amino acid polymers in which one or more amino acids arechemical analogues of a corresponding naturally-occurring amino acids.

A “subsequence” or “segment” when used in reference to a nucleic acid orpolypeptide refers to a sequence of nucleotides or amino acids thatcomprise a part of a longer sequence of nucleotides or amino acids(e.g., a polypeptide), respectively.

As used herein, the term “small molecule” is a non-protein based moietyincluding, but not limited to the following: (i) molecules typicallyless than 10 K molecular weight; (ii) molecules that are permeable tocells; (iii) molecules that are less susceptible to degradation by manycellular mechanisms than peptides or oligonucleotides; and/or (iv)molecules that generally do not elicit an immune response. Manypharmaceutical companies have extensive libraries of chemical and/orbiological mixtures, often fungal, bacterial, or algal extracts, thatwould be desirable to screen with the assays disclosed herein. Smallmolecules may be either biological or synthetic organic compounds, oreven inorganic compounds (e.g., cisplatin).

DNA Binding Proteins

Disclosed herein are methods and compositions for modulating andcontrolling stem cell differentiation using DNA binding proteins. Incertain embodiments, the DNA binding protein comprises a zinc fingerprotein (ZFP). The engineering of novel DNA binding proteins thatselectively regulate the expression of a gene at its endogenous locus(i.e., genes as they occur in the context of their natural chromosomalstructure) has been described. See, for example, WO 00/41566 and WO00/42219, the disclosures of which are incorporated by reference hereinin their entireties. This approach provides a unique capacity toselectively turn on or turn off endogenous gene expression in the celland thus affect fundamental mechanisms determining stem cell fate.

Thus, the ZFPs disclosed herein are engineered to recognize a selectedtarget site in the endogenous gene of choice. Typically, a backbone fromany suitable C₂H₂ ZFP, such as SP-1, SP-1C, or ZIF268, is used as thescaffold for the engineered ZFP (see, e.g., Jacobs, EMBO J. 11:4507(1992); Desjarlais & Berg, PNAS 90:2256-2260 (1993)). A number ofmethods can then be used to design and/or select a ZFP with highaffinity for its target (e.g., preferably with a K_(d) of less thanabout 25 nM). As described above, a ZFP can be designed or selected tobind to any suitable target site in the target endogenous gene, withhigh affinity. Co-owned PCT WO 00/42219, herein incorporated byreference in its entirety, comprehensively describes methods for design,construction, and expression of ZFPs for selected target sites.

Any suitable method known in the art can be used to design and constructnucleic acids encoding ZFPs, e.g., phage display, random mutagenesis,combinatorial libraries, computer/rational design, affinity selection,PCR, cloning from cDNA or genomic libraries, synthetic construction andthe like. (see, e.g., U.S. Pat. No. 5,786,538; Wu et al., PNAS92:344-348 (1995); Jamieson et al., Biochemistry 33:5689-5695 (1994);Rebar & Pabo, Science 263:671-673 (1994); Choo & Klug, PNAS91:11163-11167 (1994); Choo & Klug, PNAS 91: 11168-11172 (1994);Desjarlais & Berg, PNAS 90:2256-2260 (1993); Desjarlais & Berg, PNAS89:7345-7349 (1992); Pomerantz et al., Science 267:93-96 (1995);Pomerantz et al., PNAS 92:9752-9756 (1995); Liu et al., PNAS94:5525-5530 (1997); Griesman & Pabo, Science 275:657-661 (1997);Desjarlais & Berg, PNAS 91:11-99-11103 (1994)). A preferred method isdescribed in co-owned PCT WO 00/42219.

Thus, these methods work by selecting a target gene, and systematicallysearching within the possible subsequences of the gene for target sites,as described, e.g., in co-owned U.S. Pat. No. 6,453,242. In some suchmethods, every possible subsequence of 9 or 10 contiguous bases oneither strand of a potential target gene is evaluated to determinewhether it contains putative target sites, e.g., D-able sites, see U.S.Pat. No. 6,453,242. Typically, such a comparison is performed bycomputer, and a list of target sites is output. Optionally, such targetsites can be output in different subsets according to how many D-ablesites are present. It will be apparent that these principles can beextended to select target sites to be bound by ZFPs with any number ofcomponent fingers. For example, a suitable target site for a nine fingerprotein would have three component segments.

The target sites identified by the above methods can be subject tofurther evaluation by other criteria or can be used directly for designor selection (if needed) and production of a ZFP specific for such asite. A further criterion for evaluating potential target sites is theirproximity to particular regions within a gene. If a ZFP is to be used torepress a cellular gene on its own (e.g., without linking the ZFP to arepressing moiety), then the optimal location appears to be at, orwithin 50 bp upstream or downstream of the site of transcriptioninitiation, to interfere with the formation of the transcription complex(Kim & Pabo, J. Biol. Chem. 272:29795-296800 (1997)) or compete for anessential enhancer binding protein. If, however, a ZFP is fused to afunctional domain such as the KRAB repressor domain or the VP16activator domain, the location of the binding site is considerably moreflexible and can be outside known regulatory regions. For example, aKRAB domain can repress transcription at a promoter up to at least 3 kbpfrom where KRAB is bound (Margolin et al., PNAS 91:4509-4513 (1994)).Thus, target sites can be selected that do not necessarily include oroverlap segments of demonstrable biological significance with targetgenes, such as regulatory sequences. Other criteria for furtherevaluating target segments include the prior availability of ZFPsbinding to such segments or related segments, and/or ease of designingnew ZFPs to bind a given target segment.

After a target segment has been selected, a ZFP that binds to thesegment can be provided by a variety of approaches. The simplest ofapproaches is to provide a precharacterized ZFP from an existingcollection that is already known to bind to the target site. However, inmany instances, such ZFPs do not exist. An alternative approach can alsobe used to design new ZFPs, which uses the information in a database ofexisting ZFPs and their respective binding affinities. A furtherapproach is to design a ZFP based on substitution rules. See, e.g., WO96/06166; WO 98/53058; WO 98/53059 and WO 98/53060. A still furtheralternative is to select a ZFP with specificity for a given target by anempirical process such as phage display. See, e.g., WO 98/53057. In somesuch methods, each component finger of a ZFP is designed or selectedindependently of other component fingers. For example, each finger canbe obtained from a different preexisting ZFP or each finger can besubject to separate randomization and selection.

Once a ZFP has been selected, designed, or otherwise provided to a giventarget segment, the ZFP (or the DNA encoding it) is synthesized.Exemplary methods for synthesizing and expressing DNA encoding zincfinger proteins are described below. The ZFP or a polynucleotideencoding it can then be used for modulation of expression, or analysisof the target gene containing the target site to which the ZFP binds.

Expression and Purification of ZFPs

ZFP polypeptides and nucleic acids can be made using routine techniquesin the field of recombinant genetics. Basic texts disclosing the generalmethods of use in the field include Sambrook et al., Molecular Cloning,A Laboratory Manual (2nd ed. 1989); Kriegler, Gene Transfer andExpression: A Laboratory Manual (1990); and Current Protocols inMolecular Biology (Ausubel et al., eds., 1994)). In addition,essentially any nucleic acid can be custom ordered from any of a varietyof commercial sources. Similarly, peptides and antibodies can be customordered from any of a variety of commercial sources.

Two alternative methods are typically used to create the codingsequences required to express newly designed DNA-binding peptides. Oneprotocol is a PCR-based assembly procedure that utilizes six overlappingoligonucleotides (FIG. 1). Three oligonucleotides (oligos 1, 3, and 5 inFIG. 1) correspond to “universal” sequences that encode portions of theDNA-binding domain between the recognition helices. Theseoligonucleotides remain constant for all zinc finger constructs. Theother three “specific” oligonucleotides (oligos 2, 4, and 6 in FIG. 1)are designed to encode the recognition helices. These oligonucleotidescontain substitutions primarily at positions-1, 2, 3 and 6 on therecognition helices making them specific for each of the differentDNA-binding domains.

The PCR synthesis is carried out in two steps. First, a double strandedDNA template is created by combining the six oligonucleotides (threeuniversal, three specific) in a four cycle PCR reaction with a lowtemperature annealing step, thereby annealing the oligonucleotides toform a DNA “scaffold.” The gaps in the scaffold are filled in byhigh-fidelity thermostable polymerase, the combination of Taq and Pfupolymerases also suffices. In the second phase of construction, the zincfinger template is amplified by external primers designed to incorporaterestriction sites at either end for cloning into a shuttle vector ordirectly into an expression vector.

An alternative method of cloning the newly designed DNA-binding proteinsrelies on annealing complementary oligonucleotides encoding the specificregions of the desired ZFP. This particular application requires thatthe oligonucleotides be phosphorylated prior to the final ligation step.This is usually performed before setting up the annealing reactions, butkinasing can also occur post-annealing. In brief, the “universal”oligonucleotides encoding the constant regions of the proteins (oligos1, 2 and 3 of above) are annealed with their complementaryoligonucleotides. Additionally, the “specific” oligonucleotides encodingthe finger recognition helices are annealed with their respectivecomplementary oligonucleotides. These complementary oligos are designedto fill in the region that was previously filled in by polymerase in theprotocol described above. The complementary oligos to the common oligos1 and finger 3 are engineered to leave overhanging sequences specificfor the restriction sites used in cloning into the vector of choice. Thesecond assembly protocol differs from the initial protocol in thefollowing aspects: the “scaffold” encoding the newly designed ZFP iscomposed entirely of synthetic DNA thereby eliminating the polymerasefill-in step, additionally the fragment to be cloned into the vectordoes not require amplification. Lastly, the design of leavingsequence-specific overhangs eliminates the need for restriction enzymedigests of the inserting fragment.

The resulting fragment encoding the newly designed ZFP is ligated intoan expression vector. Expression vectors that are commonly utilizedinclude, but are not limited to, a modified pMAL-c2 bacterial expressionvector (New England BioLabs, “NEB”) or a eukaryotic expression vector,pcDNA (Promega).

Any suitable method of protein purification known to those of skill inthe art can be used to purify ZFPs (see Ausubel, supra, Sambrook,supra). In addition, any suitable host can be used, e.g., bacterialcells, insect cells, yeast cells, mammalian cells, and the like.

In one embodiment, expression of the ZFP fused to a maltose bindingprotein (MBP-ZFP) in bacterial strain JM109 allows for straightforwardpurification through an amylose column (NEB). High expression levels ofthe zinc finger chimeric protein can be obtained by induction with IPTGsince the MBP-ZFP fusion in the pMal-c2 expression plasmid is under thecontrol of the IPTG inducible tac promoter (NEB). Bacteria containingthe MBP-ZFP fusion plasmids are inoculated in to 2×YT medium containing10 μM ZnCl₂, 0.02% glucose, plus 50 μg/ml ampicillin and shaken at 37°C. At mid-exponential growth IPTG is added to 0.3 mM and the culturesare allowed to shake. After 3 hours the bacteria are harvested bycentrifugation, disrupted by sonication, and then insoluble material isremoved by centrifugation. The MBP-ZFP proteins are captured on anamylose-bound resin, washed extensively with buffer containing 20 mMTris-HCl (pH 7.5), 200 mM NaCl, 5 mM DTT and 50 μM ZnCl₂, then elutedwith maltose in essentially the same buffer (purification is based on astandard protocol from NEB). Purified proteins are quantitated andstored for biochemical analysis.

The biochemical properties of the purified proteins, e.g., K_(d), can becharacterized by any suitable assay. In one embodiment, K_(d) ischaracterized via electrophoretic mobility shift assays (“EMSA”)(Buratowski & Chodosh, in Current Protocols in Molecular Biology pp.12.2.1-12.2.7 (Ausubel ed., 1996); see also U.S. Pat. No. 5,789,538,co-owned PCT WO 00/42219 herein incorporated by reference in itsentirety, and Example 1). Affinity is measured by titrating purifiedprotein against a low fixed amount of labeled double-strandedoligonucleotide target. The target comprises the natural binding sitesequence (9 or 18 bp) flanked by the 3 bp found in the natural sequence.External to the binding site plus flanking sequence is a constantsequence. The annealed oligonucleotide targets possess a 1 bp 5′overhang that allows for efficient labeling of the target with T4 phagepolynucleotide kinase. For the assay the target is added at aconcentration of 40 nM or lower (the actual concentration is kept atleast 10-fold lower than the lowest protein dilution) and the reactionis allowed to equilibrate for at least 45 min. In addition the reactionmixture also contains 10 mM Tris (pH 7.5), 100 mM KCl, 1 mM MgCl₂, 0.1mM ZnCl₂, 5 mM DTT, 10% glycerol, 0.02% BSA (poly (dIdC) or (dAdT)(Pharmacia) can also added at 10-100 μg/μl).

The equilibrated reactions are loaded onto a 10% polyacrylamide gel,which has been pre-run for 45 min in Tris/glycine buffer, then bound andunbound labeled target is resolved be electrophoresis at 150V(alternatively, 10-20% gradient Tris-HCl gels, containing a 4%polyacrylamide stacker, can be used). The dried gels are visualized byautoradiography or phosphoroimaging and the apparent K_(d) is determinedby calculating the protein concentration that gives half-maximalbinding.

Similar assays can also include determining active fractions in theprotein preparations. Active fractions are determined by stoichiometricgel shifts where proteins are titrated against a high concentration oftarget DNA. Titrations are done at 100, 50, and 25% of target (usuallyat micromolar levels).

In another embodiment, phage display libraries can be used to selectZFPs with high affinity to the selected target site. This method differsfundamentally from direct design in that it involves the generation ofdiverse libraries of mutagenized ZFPs, followed by the isolation ofproteins with desired DNA-binding properties using affinity selectionmethods. To use this method, the experimenter typically proceeds asfollows.

First, a gene for a ZFP is mutagenized to introduce diversity intoregions important for binding specificity and/or affinity. In a typicalapplication, this is accomplished via randomization of a single fingerat positions −1, +2, +3, and +6, and perhaps accessory positions such as+1, +5, +8, or +10.

Next, the mutagenized gene is cloned into a phage or phagemid vector asa fusion with, e.g., gene III of filamentous phage, which encodes thecoat protein pIII. The zinc finger gene is inserted between segments ofgene III encoding the membrane export signal peptide and the remainderof pIII, so that the ZFP is expressed as an amino-terminal fusion withpIII in the mature, processed protein. When using phagemid vectors, themutagenized zinc finger gene may also be fused to a truncated version ofgene III encoding, minimally, the C-terminal region required forassembly of pIII into the phage particle.

The resultant vector library is transformed into E. coli and used toproduce filamentous phage that express variant ZFPs on their surface asfusions with the coat protein pIII (if a phagemid vector is used, thenthe this step requires superinfection with helper phage). The phagelibrary is then incubated with target DNA site, and affinity selectionmethods are used to isolate phage that bind target with high affinityfrom bulk phage. Typically, the DNA target is immobilized on a solidsupport, which is then washed under conditions sufficient to remove allbut the tightest binding phage. After washing, any phage remaining onthe support are recovered via elution under conditions that totallydisrupt zinc finger-DNA binding.

Recovered phage are used to infect fresh E. coli, which is thenamplified and used to produce a new batch of phage particles. Thebinding and recovery steps are then repeated as many times as isnecessary to sufficiently enrich the phage pool for tight binders suchthat these may be identified using sequencing and/or screening methods.

Regulatory Domains

Binding domains (e.g., ZFPs) can optionally be associated withregulatory domains (e.g., functional domains) for modulation of geneexpression. The ZFP can be covalently or non-covalently associated withone or more regulatory domains, alternatively two or more regulatorydomains, with the two or more domains being two copies of the samedomain, or two different domains. The regulatory domains can becovalently linked to the ZFP, e.g., via an amino acid linker, as part ofa fusion protein. The ZFPs can also be associated with a regulatorydomain via a non-covalent dimerization domain, e.g., a leucine zipper, aSTAT protein N terminal domain, or an FK506 binding protein (see, e.g.,O'Shea, Science 254: 539 (1991), Barahmand-Pour et al., Curr. Top.Microbiol. Immunol. 211:121-128 (1996); Klemm et al., Annu. Rev.Immunol. 16:569-592 (1998); Klemm et al., Annu. Rev. Immunol. 16:569-592(1998); Ho et al., Nature 382:822-826 (1996); and Pomeranz et al.,Biochem. 37:965 (1998)). The regulatory domain can be associated withthe ZFP at any suitable position, including the C- or N-terminus of theZFP.

Common regulatory domains for addition to the ZFP include, e.g.,effector domains from transcription factors (activators, repressors,co-activators, co-repressors), silencers, nuclear hormone receptors,oncogene transcription factors (e.g., myc, jun, fos, myb, max, mad, rel,ets, bcl, myb, mos family members etc.); DNA repair enzymes and theirassociated factors and modifiers; DNA rearrangement enzymes and theirassociated factors and modifiers; chromatin associated proteins andtheir modifiers (e.g., kinases, acetylases and deacetylases); and DNAmodifying enzymes (e.g., methyltransferases, topoisomerases, helicases,ligases, kinases, phosphatases, polymerases, endonucleases) and theirassociated factors and modifiers.

Transcription factor polypeptides from which one can obtain a regulatorydomain include those that are involved in regulated and basaltranscription. Such polypeptides include transcription factors, theireffector domains, coactivators, silencers, nuclear hormone receptors(see, e.g., Goodrich et al., Cell 84:825-30 (1996) for a review ofproteins and nucleic acid elements involved in transcription;transcription factors in general are reviewed in Barnes & Adcock, Clin.Exp. Allergy 25 Suppl. 2:46-9 (1995) and Roeder, Methods Enzymol.273:165-71 (1996)). Databases dedicated to transcription factors areknown (see, e.g., Science 269:630 (1995)). Nuclear hormone receptortranscription factors are described in, for example, Rosen et al., J.Med. Chem. 38:4855-74 (1995). The C/EBP family of transcription factorsare reviewed in Wedel et al., Immunobiology 193:171-85 (1995).Coactivators and co-repressors that mediate transcription regulation bynuclear hormone receptors are reviewed in, for example, Meier, Eur. J.Endocrinol. 134(2):158-9 (1996); Kaiser et al., Trends Biochem. Sci.21:342-5 (1996); and Utley et al., Nature 394:498-502 (1998)). GATAtranscription factors, which are involved in regulation ofhematopoiesis, are described in, for example, Simon, Nat. Genet. 11:9-11(1995); Weiss et al., Exp. Hematol. 23:99-107. TATA box binding protein(TBP) and its associated TAF polypeptides (which include TAF30, TAF55,TAF80, TAF110, TAF150, and TAF250) are described in Goodrich & Tijan,Curr. Opin. Cell Biol. 6:403-9 (1994) and Hurley, Curr. Opin. Struct.Biol. 6:69-75 (1996). The STAT family of transcription factors arereviewed in, for example, Barahmand-Pour et al., Curr. Top. Microbiol.Immunol. 211:121-8 (1996). Transcription factors involved in disease arereviewed in Aso et al., J. Clin. Invest. 97:1561-9 (1996).

In one embodiment, the KRAB repression domain from the human KOX-1protein is used as a transcriptional repressor (Thiesen et al., NewBiologist 2:363-374 (1990); Margolin et al., PNAS 91:4509-4513 (1994);Pengue et al., Nucl. Acids Res. 22:2908-2914 (1994); Witzgall et al.,PNAS 91:4514-4518 (1994)). In another embodiment, KAP-1, a KRABco-repressor, is used with KRAB (Friedman et al., Genes Dev.10:2067-2078 (1996)). Alternatively, KAP-1 can be used alone with a ZFP.Other preferred transcription factors and transcription factor domainsthat act as transcriptional repressors include MAD (see, e.g., Sommer etal., J. Biol. Chem. 273:6632-6642 (1998); Gupta et al., Oncogene16:1149-1159 (1998); Queva et al., Oncogene 16:967-977 (1998); Larssonet al., Oncogene 15:737-748 (1997); Laherty et al., Cell 89:349-356(1997); and Cultraro et al., Mol Cell. Biol. 17:2353-2359 (19977)); FKHR(forkhead in rhapdosarcoma gene; Ginsberg et al., Cancer Res.15:3542-3546 (1998); Epstein et al., Mol. Cell. Biol. 18:4118-4130(1998)); EGR-1 (early growth response gene product-1; Yan et al., PNAS95:8298-8303 (1998); and Liu et al., Cancer Gene Ther. 5:3-28 (1998));the ets2 repressor factor repressor domain (ERD; Sgouras et al., EMBO J.14:4781-4793 ((19095)); and the MAD smSIN3 interaction domain (SID; Ayeret al., Mol. Cell. Biol. 16:5772-5781 (1996)).

In one embodiment, the HSV VP16 activation domain is used as atranscriptional activator (see, e.g., Hagmann et al., J. Virol.71:5952-5962 (1997)). Other preferred transcription factors that couldsupply activation domains include the VP64 activation domain (Seipel etal., EMBO J. 11:4961-4968 (1996)); nuclear hormone receptors (see, e.g.,Torchia et al., Curr. Opin. Cell. Biol. 10:373-383 (1998)); the p65subunit of nuclear factor kappa B (Bitko & Barik, J. Virol. 72:5610-5618(1998) and Doyle & Hunt, Neuroreport 8:2937-2942 (1997)); and EGR-1(early growth response gene product-1; Yan et al., PNAS 95:8298-8303(1998); and Liu et al., Cancer Gene Ther. 5:3-28 (1998)).

Kinases, phosphatases, and other proteins that modify polypeptidesinvolved in gene regulation are also useful as regulatory domains forZFPs. Such modifiers are often involved in switching on or offtranscription mediated by, for example, hormones. Kinases involved intranscription regulation are reviewed in Davis, Mol. Reprod. Dev.42:459-67 (1995), Jackson et al., Adv. Second Messenger PhosphoproteinRes. 28:279-86 (1993), and Boulikas, Crit. Rev. Eukaryot. Gene Expr.5:1-77 (1995), while phosphatases are reviewed in, for example,Schonthal & Semin, Cancer Biol. 6:239-48 (1995). Nuclear tyrosinekinases are described in Wang, Trends Biochem. Sci. 19:373-6 (1994).

As described, useful domains can also be obtained from the gene productsof oncogenes (e.g., myc, jun, fos, myb, max, mad, rel, ets, bcl, myb,mos family members) and their associated factors and modifiers.Oncogenes are described in, for example, Cooper, Oncogenes, 2nd ed., TheJones and Bartlett Series in Biology, Boston, Mass., Jones and BartlettPublishers, 1995. The ets transcription factors are reviewed in Waslylket al., Eur. J. Biochem. 211:7-18 (1993) and Crepieux et al., Crit. Rev.Oncog. 5:615-38 (1994). Myc oncogenes are reviewed in, for example, Ryanet al., Biochem. J. 314:713-21 (1996). The jun and fos transcriptionfactors are described in, for example, The Fos and Jun Families ofTranscription Factors, Angel & Herrlich, eds. (1994). The max oncogeneis reviewed in Hurlin et al., Cold Spring Harb. Symp. Quant. Biol.59:109-16. The myb gene family is reviewed in Kanei-Ishii et al., Curr.Top. Microbiol. Immunol. 211:89-98 (1996). The mos family is reviewed inYew et al., Curr. Opin. Genet. Dev. 3:19-25 (1993).

ZFPs can include regulatory domains obtained from DNA repair enzymes andtheir associated factors and modifiers. DNA repair systems are reviewedin, for example, Vos, Curr. Opin. Cell Biol. 4:385-95 (1992); Sancar,Ann. Rev. Genet. 29:69-105 (1995); Lehmann, Genet. Eng. 17:1-19 (1995);and Wood, Ann. Rev. Biochem. 65:135-67 (1996). DNA rearrangement enzymesand their associated factors and modifiers can also be used asregulatory domains (see, e.g., Gangloff et al., Experientia 50:261-9(1994); Sadowski, FASEB J. 7:760-7 (1993)).

Similarly, regulatory domains can be derived from DNA modifying enzymes(e.g., DNA methyltransferases, topoisomerases, helicases, ligases,kinases, phosphatases, polymerases) and their associated factors andmodifiers. Helicases are reviewed in Matson et al., Bioessays, 16:13-22(1994), and methyltransferases are described in Cheng, Curr. Opin.Struct. Biol. 5:4-10 (1995). Chromatin associated proteins and theirmodifiers (e.g., kinases, acetylases and deacetylases), such as histonedeacetylase (Wolffe, Science 272:371-2 (1996)) are also useful asdomains for addition to the ZFP of choice. In one preferred embodiment,the regulatory domain is a DNA methyl transferase that acts as atranscriptional repressor (see, e.g., Van den Wyngaert et al., FEBSLett. 426:283-289 (1998); Flynn et al., J. Mol. Biol. 279:101-116(1998); Okano et al., Nucleic Acids Res. 26:2536-2540 (1998); and Zardo& Caiafa, J. Biol. Chem. 273:16517-16520 (1998)). In another preferredembodiment, endonucleases such as Fok1 are used as transcriptionalrepressors, which act via gene cleavage (see, e.g., WO95/09233; andPCT/US94/01201).

Factors that control chromatin and DNA structure, movement andlocalization and their associated factors and modifiers; factors derivedfrom microbes (e.g., prokaryotes, eukaryotes and virus) and factors thatassociate with or modify them can also be used to obtain chimericproteins. In one embodiment, recombinases and integrases are used asregulatory domains. In one embodiment, histone acetyltransferase is usedas a transcriptional activator (see, e.g., Jin & Scotto, Mol. Cell.Biol. 18:4377-4384 (1998); Wolffe, Science 272:371-372 (1996); Tauntonet al., Science 272:408-411 (1996); and Hassig et al., PNAS 95:3519-3524(1998)). In another embodiment, histone deacetylase is used as atranscriptional repressor (see, e.g., Jin & Scotto, Mol. Cell. Biol.18:4377-4384 (1998); Syntichaki & Thireos, J. Biol. Chem.273:24414-24419 (1998); Sakaguchi et al., Genes Dev. 12:2831-2841(1998); and Martinez et al., J. Biol. Chem. 273:23781-23785 (1998)).

Another suitable repression domain is methyl binding domain protein 2B(MBD-2B) (see, also Hendrich et al. (1999) Mamm Genome 10:906-912 fordescription of MBD proteins). Another useful repression domain is thatassociated with the v-ErbA protein (see infra). See, for example, Damm,et al. (1989) Nature 339:593-597; Evans (1989) Int. J. Cancer Suppl.4:26-28; Pain et al. (1990) New Biol. 2:284-294; Sap et al. (1989)Nature 340:242-244; Zenke et al. (1988) Cell 52:107-119; and Zenke etal. (1990) Cell 61:1035-1049. Additional exemplary repression domainsinclude, but are not limited to, thyroid hormone receptor (TR, seeinfra), SID, MBD1, MBD2, MBD3, MBD4, MBD-like proteins, members of theDNMT family (e.g., DNMT1, DNMT3A, DNMT3B), Rb, MeCP1 and MeCP2. See, forexample, Bird et al. (1999) Cell 99:451-454; Tyler et al. (1999) Cell99:443-446; Knoepfler et al. (1999) Cell 99:447-450; and Robertson etal. (2000) Nature Genet. 25:338-342. Additional exemplary repressiondomains include, but are not limited to, ROM2 and AtHD2A. See, forexample, Chern et al. (1996) Plant Cell 8:305-321; and Wu et al. (2000)Plant 22:19-27.

Certain members of the nuclear hormone receptor (NHR) superfamily,including, for example, thyroid hormone receptors (TRs) and retinoicacid receptors (RARs) are among the most potent transcriptionalregulators currently known. Zhang et al., Annu. Rev. Physiol. 62:439-466(2000) and Sucov et al., Mol Neurobiol 10(2-3):169-184 (1995). In theabsence of their cognate ligand, these proteins bind with highspecificity and affinity to short stretches of DNA (e.g., 12-17 basepairs) within regulatory loci (e.g., enhancers and promoters) and effectrobust transcriptional repression of adjacent genes. The potency oftheir regulatory action stems from the concurrent use of two distinctfunctional pathways to drive gene silencing: (i) the creation of alocalized domain of repressive chromatin via the targeting of a complexbetween the corepressor N-CoR and a histone deacetylase, HDAC3 (Guentheret al., Genes Dev 14:1048-1057 (2000); Urnov et al., EMBO J 19:4074-4090(2000); Li et al., EMBO J 19, 4342-4350 (2000) and Underhill et al., J.Biol. Chem. 275:40463-40470 (2000)) and (ii) a chromatin-independentpathway (Urnov et al., supra) that may involve direct interference withthe function of the basal transcription machinery (Fondell et al., GenesDev 7(7B):1400-1410 (1993) and Fondell et al., Mol Cell Biol 16:281-287(1996).

In the presence of very low (e.g., nanomolar) concentrations of theirligand, these receptors undergo a conformational change that leads tothe release of corepressors, recruitment of a different class ofauxiliary molecules (e.g., coactivators) and potent transcriptionalactivation. Collingwood et al., J. Mol. Endocrinol. 23(3):255-275(1999).

The portion of the receptor protein responsible for transcriptionalcontrol (e.g., repression and activation) can be physically separatedfrom the portion responsible for DNA binding, and retains fullfunctionality when tethered to other polypeptides, for example, otherDNA-binding domains. Accordingly, a nuclear hormone receptortranscription control domain can be fused to a ZFP DNA-binding domainsuch that the transcriptional regulatory activity of the receptor can betargeted to a chromosomal region of interest (e.g., a gene) by virtue ofthe ZFP binding domain.

Moreover, the structure of TR and other nuclear hormone receptors can bealtered, either naturally or through recombinant techniques, such thatit loses all capacity to respond to hormone (thus losing its ability todrive transcriptional activation), but retains the ability to effecttranscriptional repression. This approach is exemplified by thetranscriptional regulatory properties of the oncoprotein v-ErbA. Thev-ErbA protein is one of the two proteins required for leukemictransformation of immature red blood cell precursors in young chicks bythe avian erythroblastosis virus. TR is a major regulator oferythropoiesis (Beug et al., Biochim Biophys Acta 1288(3):M35-47 (1996);in particular, in its unliganded state, it represses genes required forcell cycle arrest and the differentiated state. Thus, the administrationof thyroid hormone to immature erythroblasts leads to their rapiddifferentiation. The v-ErbA oncoprotein is an extensively mutatedversion of TR; these mutations include: (i) deletion of 12amino-terminal amino acids; (ii) fusion to the gag oncoprotein; (iii)several point mutations in the DNA binding domain that alter the DNAbinding specificity of the protein relative to its parent, TR, andimpair its ability to heterodimerize with the retinoid X receptor; (iv)multiple point mutations in the ligand-binding domain of the proteinthat effectively eliminate the capacity to bind thyroid hormone; and (v)a deletion of a carboxy-terminal stretch of amino acids that isessential for transcriptional activation. Stunnenberg et al., BiochimBiophys Acta 1423(1):F15-33 (1999). As a consequence of these mutations,v-ErbA retains the capacity to bind to naturally occurring TR targetgenes and is an effective transcriptional repressor when bound (Urnov etal., supra; Sap et al., Nature 340:242-244 (1989); and Ciana et al.,EMBO J. 17(24):7382-7394 (1999). In contrast to TR, however, v-ErbA iscompletely insensitive to thyroid hormone, and thus maintainstranscriptional repression in the face of a challenge from anyconcentration of thyroids or retinoids, whether endogenous to themedium, or added by the investigator (4).

We have previously demonstrated that this functional property of v-ErbAis retained when its repression domain is fused to a heterologous,synthetic DNA binding domain. Accordingly, in one aspect, v-ErbA or itsfunctional fragments are used as a repression domain. In additionalembodiments, TR or its functional domains are used as a repressiondomain in the absence of ligand and/or as an activation domain in thepresence of ligand (e.g., 3,5,3′-triiodo-L-thyronine or T3). Thus, TRcan be used as a switchable functional domain (e.g., a bifunctionaldomain); its activity (activation or repression) being dependent uponthe presence or absence (respectively) of ligand.

Additional exemplary repression domains are obtained from the DAXprotein and its functional fragments. Zazopoulos et al., Nature390:311-315 (1997). In particular, the C-terminal portion of DAX-1,including amino acids 245-470, has been shown to possess repressionactivity. Altincicek et al., J. Biol. Chem. 275:7662-7667 (2000). Afurther exemplary repression domain is the RBP1 protein and itsfunctional fragments. Lai et al., Oncogene 18:2091-2100 (1999); Lai etal., Mol. Cell. Biol. 19:6632-6641 (1999); Lai et al., Mol. Cell. Biol.21:2918-2932 (2001) and WO 01/04296. The full-length RBP1 polypeptidecontains 1257 amino acids. Exemplary functional fragments of RBP1 are apolypeptide comprising amino acids 1114-1257, and a polypeptidecomprising amino acids 243-452.

Members of the TIEG family of transcription factors contain threerepression domains known as R1, R2 and R3. Repression by TIEG familyproteins is achieved at least in part through recruitment of mSIN3Ahistone deacetylases complexes. Cook et al. (1999) J. Biol. Chem.274:29,500-29,504; Zhang et al. (2001) Mol. Cell. Biol. 21:5041-5049.Any or all of these repression domains (or their functional fragments)can be fused alone, or in combination with additional repression domains(or their functional fragments), to a DNA-binding domain to generate atargeted exogenous repressor molecule.

Furthermore, the product of the human cytomegalovirus (HCMV) UL34 openreading frame acts as a transcriptional repressor of certain HCMV genes,for example, the US3 gene. LaPierre et al. (2001) J. Virol.75:6062-6069. Accordingly, the UL34 gene product, or functionalfragments thereof, can be used as a component of a fusion polypeptidealso comprising a zinc finger binding domain. Nucleic acids encodingsuch fusions are also useful in the methods and compositions disclosedherein.

Yet another exemplary repression domain is the CDF-1 transcriptionfactor and/or its functional fragments. See, for example, WO 99/27092.

The Ikaros family of proteins are involved in the regulation oflymphocyte development, at least in part by transcriptional repression.Accordingly, an Ikaros family member (e.g., Ikaros, Aiolos) or afunctional fragment thereof, can be used as a repression domain. See,for example, Sabbattini et al. (2001) EMBO J. 20:2812-2822.

The yeast Ashlp protein comprises a transcriptional repression domain.Maxon et al. (2001) Proc. Natl. Acad. Sci. USA 98:1495-1500.Accordingly, the Ashlp protein, its functional fragments, and homologuesof Ashlp, such as those found, for example, in, vertebrate, mammalian,and plant cells, can serve as a repression domain for use in the methodsand compositions disclosed herein.

Additional exemplary repression domains include those derived fromhistone deacetylases (HDACs, e.g., Class I HDACs, Class II HDACs, SIR-2homologues), HDAC-interacting proteins (e.g., SIN3, SAP30, SAP15, NCoR,SMRT, RB, p107, p130, RBAP46/48, MTA, Mi-2, Brg1, Brm), DNA-cytosinemethyltransferases (e.g., Dnmt1, Dnmt3a, Dnmt3b), proteins that bindmethylated DNA (e.g., MBD1, MBD2, MBD3, MBD4, MeCP2, DMAP1), proteinmethyltransferases (e.g., lysine and arginine methylases, SuVarhomologues such as Suv39H1), polycomb-type repressors (e.g., Bmi-1,eed1, RING1, RYBP, E2F6, Mel18, YY1 and CtBP), viral repressors (e.g.,adenovirus E1b 55K protein, cytomegalovirus UL34 protein, viraloncogenes such as v-erbA), hormone receptors (e.g., Dax-1, estrogenreceptor, thyroid hormone receptor), and repression domains associatedwith naturally-occurring zinc finger proteins (e.g., WT1, KAP1). Furtherexemplary repression domains include members of the polycomb complex andtheir homologues, HPH1, HPH2, HPC2, NC2, groucho, Eve, tramtrak, mHP1,SIP1, ZEB1, ZEB2, and Enx1/Ezh2. In all of these cases, either thefull-length protein or a functional fragment can be used as a repressiondomain for fusion to a zinc finger binding domain. Furthermore, anyhomologues of the aforementioned proteins can also be used as repressiondomains, as can proteins (or their functional fragments) that interactwith any of the aforementioned proteins.

Additional repression domains, and exemplary functional fragments, areas follows. Hes1 is a human homologue of the Drosophila hairy geneproduct and comprises a functional fragment encompassing amino acids910-1014. In particular, a WRPW (trp-arg-pro-trp) motif can act as arepression domain. Fisher et al. (1996) Mol. Cell. Biol. 16:2670-2677.

The TLE1, TLE2 and TLE3 proteins are human homologues of the Drosophilagroucho gene product. Functional fragments of these proteins possessingrepression activity reside between amino acids 1-400. Fisher et al.,supra.

The Tbx3 protein possesses a functional repression domain between aminoacids 524-721. He et al. (1999) Proc. Natl. Acad. Sci. USA96:10,212-10,217. The Tbx2 gene product is involved in repression of thep14/p16 genes and contains a region between amino acids 504-702 that ishomologous to the repression domain of Tbx3; accordingly Tbx2 and/orthis functional fragment can be used as a repression domain. Carreira etal. (1998) Mol. Cell. Biol. 18:5,099-5,108.

The human Ezh2 protein is a homologue of Drosophila enhancer of zesteand recruits the eed1 polycomb-type repressor. A region of the Ezh2protein comprising amino acids 1-193 can interact with eed1 and represstranscription; accordingly Ezh2 and/or this functional fragment can beused as a repression domain. Denisenko et al. (1998) Mol. Cell. Biol.18:5634-5642.

The RYBP protein is a corepressor that interacts with polycomb complexmembers and with the YY1 transcription factor. A region of RYBPcomprising amino acids 42-208 has been identified as functionalrepression domain. Garcia et al. (1999) EMBO J. 18:3404-3418.

The RING finger protein RING1A is a member of two different vertebratepolycomb-type complexes, contains multiple binding sites for variouscomponents of the polycomb complex, and possesses transcriptionalrepression activity. Accordingly, RING1A or its functional fragments canserve as a repression domain. Satjin et al. (1997) Mol. Cell. Biol.17:4105-4113.

The Bmi-1 protein is a member of a vertebrate polycomb complex and isinvolved in transcriptional silencing. It contains multiple bindingsites for various polycomb complex components. Accordingly, Bmi-1 andits functional fragments are useful as repression domains. Gunster etal. (1997) Mol. Cell. Biol. 17:2326-2335; Hemenway et al. (1998)Oncogene 16:2541-2547.

The E2F6 protein is a member of the mammalian Bmi-1-containing polycombcomplex and is a transcriptional repressor that is capable or recruitingRYBP, Bmi-1 and RING1A. A functional fragment of E2F6 comprising aminoacids 129-281 acts as a transcriptional repression domain. Accordingly,E2F6 and its functional fragments can be used as repression domains.Trimarchi et al. (2001) Proc Natl. Acad. Sci. USA 98:1519-1524.

The eed1 protein represses transcription at least in part throughrecruitment of histone deacetylases (e.g., HDAC2). Repression activityresides in both the N- and C-terminal regions of the protein.Accordingly, eed1 and its functional fragments can be used as repressiondomains. van der Vlag et al. (1999) Nature Genet. 23:474-478.

The CTBP2 protein represses transcription at least in part throughrecruitment of an HPC2-polycomb complex. Accordingly, CTBP2 and itsfunctional fragments are useful as repression domains. Richard et al.(1999) Mol. Cell. Biol. 19:777-787.

Neuron-restrictive silencer factors are proteins that repress expressionof neuron-specific genes. Accordingly, a NRSF or functional fragmentthereof can serve as a repression domain. See, for example, U.S. Pat.No. 6,270,990.

It will be clear to those of skill in the art that, in the formation ofa fusion protein (or a nucleic acid encoding same) between a zinc fingerbinding domain and a functional domain, either a repressor or a moleculethat interacts with a repressor is suitable as a functional domain.Essentially any molecule capable of recruiting a repressive complexand/or repressive activity (such as, for example, histone deacetylation)to the target gene is useful as a repression domain of a fusion protein.

Additional exemplary activation domains include, but are not limited to,p300, CBP, PCAF, SRC1 PvALF, AtHD2A and ERF-2. See, for example, Robyret al. (2000) Mol. Endocrinol. 14:329-347; Collingwood et al. (1999) J.Mol. Endocrinol. 23:255-275; Leo et al. (2000) Gene 245:1-11;Manteuffel-Cymborowska (1999) Acta Biochim. Pol. 46:77-89; McKenna etal. (1999) J. Steroid Biochem. Mol. Biol. 69:3-12; Malik et al. (2000)Trends Biochem. Sci. 25:277-283; and Lemon et al. (1999) Curr. Opin.Genet. Dev. 9:499-504. Additional exemplary activation domains include,but are not limited to, OsGAI, HALF-1, C1, AP1, ARF-5, -6, -7, and -8,CPRF1, CPRF4, MYC-RP/GP, and TRAB1. See, for example, Ogawa et al.(2000) Gene 245:21-29; Okanami et al. (1996) Genes Cells 1:87-99; Goffet al. (1991) Genes Dev. 5:298-309; Cho et al. (1999) Plant Mol. Biol.40:419-429; Ulmason et al. (1999) Proc. Natl. Acad. Sci. USA96:5844-5849; Sprenger-Haussels et al. (2000) Plant J. 22:1-8; Gong etal. (1999) Plant Mol. Biol. 41:33-44; and Hobo et al. (1999) Proc. Natl.Acad. Sci. USA 96:15, 348-15,353.

It will be clear to those of skill in the art that, in the formation ofa fusion protein (or a nucleic acid encoding same) between a zinc fingerbinding domain and a functional domain, either an activator or amolecule that interacts with an activator is suitable as a functionaldomain. Essentially any molecule capable of recruiting an activatingcomplex and/or activating activity (such as, for example, histoneacetylation) to the target gene is useful as an activating domain of afusion protein.

Insulator domains, chromatin remodeling proteins such as ISWI-containingdomains and/or methyl binding domain proteins suitable for use asfunctional domains in fusion molecules are described, for example, inco-owned PCT application US01/40616 and co-owned U.S. Patentapplications 60/236,409; 60/236,884; and 60/253,678.

In a further embodiment, a DNA-binding domain (e.g., a zinc fingerdomain) is fused to a bifunctional domain (BFD). A bifunctional domainis a transcriptional regulatory domain whose activity depends uponinteraction of the BFD with a second molecule. The second molecule canbe any type of molecule capable of influencing the functional propertiesof the BFD including, but not limited to, a compound, a small molecule,a peptide, a protein, a polysaccharide or a nucleic acid. An exemplaryBFD is the ligand binding domain of the estrogen receptor (ER). In thepresence of estradiol, the ER ligand binding domain acts as atranscriptional activator; while, in the absence of estradiol and thepresence of tamoxifen or 4-hydroxy-tamoxifen, it acts as atranscriptional repressor. Another example of a BFD is the thyroidhormone receptor (TR) ligand binding domain which, in the absence ofligand, acts as a transcriptional repressor and in the presence ofthyroid hormone (T3), acts as a transcriptional activator. An additionalBFD is the glucocorticoid receptor (GR) ligand binding domain. In thepresence of dexamethasone, this domain acts as a transcriptionalactivator; while, in the presence of RU486, it acts as a transcriptionalrepressor. An additional exemplary BFD is the ligand binding domain ofthe retinoic acid receptor. In the presence of its ligandall-trans-retinoic acid, the retinoic acid receptor recruits a number ofco-activator complexes and activates transcription. In the absence ofligand, the retinoic acid receptor is not capable of recruitingtranscriptional co-activators. Additional BFDs are known to those ofskill in the art. See, for example, U.S. Pat. Nos. 5,834,266 and5,994,313 and PCT WO 99/10508.

Linker domains between polypeptide domains, e.g., between two ZFPs orbetween a ZFP and a regulatory domain, can be included. Such linkers aretypically polypeptide sequences, such as poly gly sequences of betweenabout 5 and 200 amino acids. Preferred linkers are typically flexibleamino acid subsequences which are synthesized as part of a recombinantfusion protein. For example, in one embodiment, the linker DGGGS is usedto link two ZFPs. In another embodiment, the flexible linker linking twoZFPs is an amino acid subsequence comprising the sequence TGEKP (see,e.g., Liu et al., PNAS 5525-5530 (1997)). In another embodiment, thelinker LRQKDGERP is used to link two ZFPs. In another embodiment, thefollowing linkers are used to link two ZFPs: GGRR (Pomerantz et al.1995, supra), (G4S)_(n) (Kim et al., PNAS 93, 1156-1160 (1996.); andGGRRGGGS; LRQRDGERP; LRQKDGGGSERP; LRQKd(G3S)₂ ERP. Alternatively,flexible linkers can be rationally designed using computer programcapable of modeling both DNA-binding sites and the peptides themselves(Desjarlais & Berg, PNAS 90:2256-2260 (1993), PNAS 91:11099-11103 (1994)or by phage display methods.

In other embodiments, a chemical linker is used to connect syntheticallyor recombinantly produced domain sequences. Such flexible linkers areknown to persons of skill in the art. For example, poly(ethylene glycol)linkers are available from Shearwater Polymers, Inc. Huntsville, Ala.These linkers optionally have amide linkages, sulfhydryl linkages, orheterofunctional linkages. In addition to covalent linkage of ZFPs toregulatory domains, non-covalent methods can be used to producemolecules with ZFPs associated with regulatory domains.

In addition to regulatory domains, often the ZFP is expressed as afusion protein such as maltose binding protein (“MBP”), glutathione Stransferase (GST), hexahistidine, c-myc, and the FLAG epitope, for easeof purification, monitoring expression, or monitoring cellular andsubcellular localization.

Identification

One or more the following techniques can be used to identify and/orcharacterize ZFPs suitable for use in the presently disclosed methodsand compositions:

(i) DNA Sequencing: relevant genomic DNA sequence (human and mouse) fora target gene (whose expression is to be regulated) are identified.(See, also, exemplary target genes discussed below). Typically,approximately 1-2 kilobases of sequence on either side of thetranscription initiation site is obtained. Sequences may be availablefrom public databases, or can be cloned from genomic DNA and sequencedaccording to techniques that are well known in the art. Thetranscription initiation site of each gene may also be identified, forexample, using 5′-RACE;

(ii) DNaseI hypersensitivity mapping may be optionally employed, forexample to characterize the chromatin structure in the promoter regionsof the target genes (e.g., in mouse ES cells and/or human embryonic andadult stem cells). Parallel DNaseI mapping may be performed inimmortalized mouse and human cell lines (e.g., MES13 and HEK293,respectively), which serve as useful models in which to validate andoptimize DNaseI mapping probes, and to screen ZFP-TFs for their capacityto regulate target gene expression (prior to performing these analysesin stem cells);

(iii) Design of ZFPs: ZFP-TFs that selectively bind to sites in thetarget gene(s) (e.g., DNaseI accessible regions) are designed followingthe teachings herein. The effectiveness of the ZFP-TFs in regulatinggene expression is determined, for example by introducing them, or bytransfecting polynucleotides encoding them, into the immortalized celllines and measuring mRNA expression from the target gene by real-timePCR (e.g., TaqMan®). Different transcription regulatory domains may betested on each ZFP to optimize activity. ZFPs may be designed as mimicsof “decision-making” transcription factors, e.g., Gli, which is actedupon by sonic hedgehog (Shh), known positive regulators of SCproliferation ex vivo. See, e.g., Bhardwaj et al. Nat Immunol 2001,2:172-180; Villavicencio et al. Am J Hum Genet 2000, 67:1047-1054. Forinstance, a ZFP may be designed as a “Gli-3 mimic” to prevent or reducethe activation of the Gli-1 promoter by Shh/Gli-3;

(iv) ZFP-TFs that have been validated in the immortalized cell lines arepreferably then tested in stem cells. Plasmids that express the ZFP-TFsare delivered to the cells, e.g., by electroporation. Other deliveryoptions that offer certain advantages (e.g., placing the ZFP-TF under aninducible promoter for controlled expression) can also be used. As withthe immortalized cell lines, the ability of ZFP-TFs to regulate geneexpression in stem cells is measured, for example, using RT-PCR analysis(Taqman); and

(v) the effects on cellular differentiation can also be examined, forexample, by analyzing the pattern of expressed markers of cell type(such as those exemplified in Table 1) using established in vitrodifferentiation protocols as described in the art and herein. One ormore cytokines (and/or other factors) that induce differentiation mayalso be included.

Alternatively, an exemplary method for identifying genes important forlineage specification is to introduce a ZFP-TF library in mouse EScells, to screen for ZFPs that promote differentiation towards specificcell lineages. A set of mouse ES cell lines, in which theβ-galactosidase marker gene has been inserted into individual mousegenes that are specifically expressed in certain cell types and tissues,including those of lymphoid lineage, have been described. See, forexample, Mitchell et al. (2001) Nature Genetics 28:241-249; Tate et al.(1998) J. Cell. Sci. 111:2575-2585; and Meth. Enzymology 328:592-615(2000). Such cell lines can be used to screen large numbers of ZFP-TFs,to identify those ZFPs that regulate, for example, lymphoid and myeloiddifferentiation. ZFP-TF function can be scored by either the staining ofcells for (3-galactosidase expression, or by assessment of morphologicaland phenotypic changes associated with differentiation. This type ofscreen allows the generation of 500 cell lines per month, with each cellline expressing a single engineered ZFP-TF. This, in turn, allows forthe identification of ZFP-TFs—and their respective target genes—that areresponsible for controlling differentiation of mouse ES cells intospecific lineages, e.g., immune cell lineages. The results of suchscreens are likely to be readily transferable to human adult stem cellsbecause promoter sequences are highly conserved across species.

Target Genes

The ZFPs described herein can be developed to target one or more genesthat may be involved in stem cell differentiation, dedifferentiation,proliferation and/or self-renewal. Suitable targets for regulation byZFPs in order to dedifferentiate and/or maintain self-renewing stem cellcultures include, but are not limited to, one or more of the genes shownin Tables 1 and 2.

Additionally, other genes involved in differentiation can also betargeted. For example, in hematopoietic stem cells, ZFPs can be targetedto repress the genes encoding E1A, EBF, Pax-5 (which is anticipated toresult in a robust proliferation of B-lymphocyte precursor cells);SCL/Tal-1, AML-1 or c-Myb (which is anticipated to result in a robustproliferation of myeloid and/or erythroid lineages); and TCF-1 (which isanticipated to result in a robust proliferation of T-cells). As shown inTable 1, liver stem cells are known express certain proteins, forexample OV6 and/or a cytokeratin such as cytokeratin 19. (See, U.S. Pat.No. 6,129,911). Expression of the GATA4 gene in embryonic stem cellspromotes differentiation into extraembryonic endoderm.

Other suitable targets may include HoxB4, which drives differentiationof embryonic stem cells into the early stage hematopoietic lineage andis a strong positive regulator of hematopoietic stem cell expansion, andconfers lymphoid-myeloid engraftment potential (see, e.g., Helgason etal. Blood 87, 2740-9. (1996); Sauvageau, G. et al. Genes Dev 9, 1753-65.(1995); Antonchuk et al. Cell 109, 39-45 (2002); Kyba et al. Cell 109,29-37 (2002); Oct-3/4, which seems to play a role in controllingembryonic and adult stem cell phenotype (see, e.g., Niwa et al. NatGenet 24, 372-6. (2000); Nichols, J. et al. Cell 95, 379-91. (1998);GCNF; Bcrp1; Sox-2; genes that promote B cell differentiation such asXBP-1, PAX5/BSAP, and Blimp-1, and those that promote NK or T celldevelopment include CBF-α2 and GATA-3. (See, e.g., Reimold et al. Nature412, 300-7. (2001); Hagman et al. Curr Top Microbiol Immunol 245, 169-94(2000); Angelin-Duclos et al. J Immunol 165, 5462-71. (2000); Telfer etal. Dev Biol 229, 363-82. (2001); Nawijn et al. J Immunol 167, 724-32.(2001).

Oct-4, for example, is known to be required for totipotency in mice andis likely required for it in humans. See, e.g., Nichols et al. Cell1998, 95:379-391; Hansis et al. Mol Hum Reprod 2000, 6:999-1004. TheOct-4 promoter has been characterized. See, e.g., Nordhoff et al. MammGenome 2001, 12:309-317. Conditional upregulation and downregulationfrom a transgene yields a well-characterized array of phenotypes. See,Niwa et al. Nat Genet 2000, 24:372-376. Similarly, another target forthe ZFPs described herein may be HES-1, a bHLH transcriptional repressorthat is activated by the Notch pathway and is required for maintenanceof proliferation of neuronal precursors, presumably by repressing thep21 gene. Castella et al. Mol Cell Biol 2000, 20:6170-6183; Solecki etal. Neuron 2001, 31:557-568.

Other gene targets for modulation by ZFPs include cytokines or othergrowth factors. For example, self-renewal of many stem cells,particularly non-human ES cells, is promoted by cytokines such asleukemia inhibitory factor (LIF). (See, U.S. Pat. No. 5,187,077). Othernon-limiting examples of genes encoding cytokines which may be targeted(alone or in combination) using the methods and compositions describedinterleukin-2 (IL-2) (Morgan et al. (1976) Science 193:1007-1008); stemcell factor (SCF); interleukin 3 (IL-3); interleukin 6 (IL-6)(Brankenhoff et al. (1987) Immunol. 139:4116-4121); interleukin 12(IL-12); G-CSF; granulocyte macrophage-colony stimulating factor(GM-CSF); interleukin-1 alpha (IL-1a); interleukin-11 (IL-11); MIP-1α;c-kit ligand, thrombopoietin (TPO); CD40 ligand (CD40L) (Spriggs et al.,(1992) J. Exp. Med. 176:1543-1550 and Armitage et al. (1992) Nature357:80-82); tumor necrosis factor-related activation-induced cytokine(TRANCE) (Wong et al. (1997) J. Biol Chem 272(40):25190-4); tumornecrosis factors (e.g., TNF-alpha, Spriggs (1992) Immunol Ser. 56:3-34);and flt3 ligand (flt-3L) (Lyman et al. (1995) Oncogene 11(6):1165-72).Growth factors involved in differentiation and self-renewal capabilitiesinclude, but are not limited to, EGF, amphiregulin, fibroblast growthfactor and transforming growth factor alpha. (See, e.g., Reynolds andWeiss (1992) Science, 255:1707; U.S. Pat. No. 6,265,175 and U.S. Pat.No. 5,851,832).

Still other gene targets for modulation by ZFPs include secreted factorsthat instruct cells to differentiate or to remain dedifferentiated.Non-limiting examples of secreted factors include, the highly conservedfamily of proteins that includes TGFbeta and Wnt regulate transcriptionof proteins such as beta-cadherin. In Drosophila, DPP (a homologue ofBmp2/4) is required to maintain female germ line stem cells and topromote cell division. Notch and related proteins also act in variousorganisms in the development of sensory organ systems.

Genes whose protein products are involved in cell-cell interactions canalso be targeted for modulation by the ZFPs described herein in order tocontrol the differentiation and culture of cells. For example, integrinsare a large family of proteins that mediate, among other things,adhesion of cells to the extracellular matrix. Molecules that formpotential targets also include laminin, demosomal glycoproteins such asdemoplakin I, cell adhesion molecules such as liver cell adhesionmolecule LCAM, carcinoembryoni antigen (CEA), dipeptidyl peptidase-4.(See, U.S. Pat. No. 6,129,911). It will be readily apparent in view ofthe teachings herein that other genes can also be targeted, alone or invarious combinations and that such targets can be readily determinedusing standard techniques.

Many of the products of these and other suitable target genes areintracellular proteins and therefore their levels could not besignificantly increased simply by addition of exogenous sources of theproteins to the culture medium. The compositions and methods describedherein allow for the independent control of expression of any targetgene(s) from within the cells to direct stem cell differentiationtowards specific immune lineages.

Table 1 summarizes markers commonly used to identify stem cells and tocharacterize differentiated cell types arising from these cells.

TABLE 1 Markers Commonly Used to Identify Stem Cells and to CharacterizeDifferentiated Cell Types Marker Name Cell Type Significance BloodVessel Fetal liver kinase-1 Endothelial Cell-surface receptor proteinthat identifies (Flk1) endothelial cell progenitor; marker of cell- cellcontacts Smooth muscle cell- Smooth muscle Identifies smooth musclecells in the wall of specific myosin heavy blood vessels chain Vascularendothelial cell Smooth muscle Identifies smooth muscle cells in thewall of cadherin blood vessels Bone Bone-specific alkaline OsateoblastEnzyme expressed in osteoblast; activity phosphatase indicates boneformation (BAP) Hydroxyapatite Osteoblast Mineralized bone matrix thatprovides structural integrity; marker of bone formation OsteocalcinOsteoblast Mineral-binding protein uniquely (OC) synthesized byosteoblast; marker of bone formation Bone Marrow and Blood Bonemorphogenetic Mesenchymal Important for the differentiation of proteinreceptor stem and committed mesenchymal cell types from (BMPR)progenitor cells mesenchymal stem and progenitor cells; BMPR identifiesearly mesenchymal lineages (stem and progenitor cells) CD4 and CD8 Whiteblood cell Cell-surface protein markers specific for (WBC) mature Tlymphocyte (WBC subtype) CD34 Hematopoietic Cell-surface protein on bonemarrow cell, stem cell (HSC), indicative of a HSC and endothelialsatellite, progenitor; CD34 also identifies muscle endothelialsatellite, a muscle stem cell progenitor CD34+Sca1+Lin− profileMesenchymal Identifies MSCs, which can differentiate stem cell (MSC)into adipocyte, osteocyte, chondrocyte, and myocyte CD38 Absent on HSCCell-surface molecule that identifies WBC Present on WBC lineages.Selection of CD34+/CD38− cells lineages allows for purification of HSCpopulations CD44 Mesenchymal A type of cell-adhesion molecule used toidentify specific types of mesenchymal cells c-Kit HSC, MSC Cell-surfacereceptor on BM cell types that identifies HSC and MSC; binding by fetalcalf serum (FCS) enhances proliferation of ES cells, HSCs, MSCs, andhematopoietic progenitor cells Colony-forming unit HSC, MSC CFU assaydetects the ability of a single (CFU) progenitor stem cell or progenitorcell to give rise to one or more cell lineages, such as red blood cell(RBC) and/or white blood cell (WBC) lineages Fibroblast colony-formingBone marrow An individual bone marrow cell that has unit fibroblastgiven rise to a colony of multipotent (CFU-F) fibroblast cells; suchidentified cells are precursors of differentiated mesenchymal lineagesHoechst dye Absent on HSC Fluorescent dye that binds DNA; HSC extrudesthe dye and stains lightly compared with other cell types Leukocytecommon antigen WBC Cell-surface protein on WBC progenitor (CD45) Lineagesurface antigen HSC, MSC Thirteen to 14 different cell-surface proteins(Lin) Differentiated that are markers of mature blood cell RBC and WBClineages; detection of Lin-negative cells lineages assists in thepurification of HSC and hematopoietic progenitor populations Mac-1 WBCCell-surface protein specific for mature granulocyte and macrophage (WBCsubtypes) Muc-18 (CD146) Bone marrow Cell-surface protein(immunoglobulin fibroblasts, superfamily) found on bone marrowendothelial fibroblasts, which may be important in hematopoiesis; asubpopulation of Muc-18+ cells are mesenchymal precursors Stem cellantigen HSC, MSC Cell-surface protein on bone marrow (BM) (Sca-1) cell,indicative of HSC and MSC Stro-1 antigen Stromal Cell-surfaceglycoprotein on subsets of bone (mesenchymal) marrow stromal(mesenchymal) cells; precursor cells, selection of Stro-1+ cells assistsin isolating hematopoietic mesenchymal precursor cells, which are cellsmultipotent cells that give rise to adipocytes, osteocytes, smoothmyocytes, fibroblasts, chondrocytes, and blood cells Thy-1 HSC, MSCCell-surface protein; negative or low detection is suggestive of HSCCartilage Collagen types II and IV Chondrocyte Structural proteinsproduces specifically by chondrocyte Keratin Keratinocyte Principalprotein of skin; identifies differentiated keratinocyte Sulfatedproteoglycan Chondrocyte Molecule found in connective tissues;synthesized by chondrocyte Fat Adipocyte lipid-binding AdipocyteLipid-binding protein located specifically in protein adipocyte (ALBP)Fatty acid transporter Adipocyte Transport molecule located specificallyin (FAT) adipocyte Adipocyte lipid-binding Adipocyte Lipid-bindingprotein located specifically in protein adipocyte (ALBP) General Ychromosome Male cells Male-specific chromosome used in labeling anddetecting donor cells in female transplant recipients Karyotype Mostcell types Analysis of chromosome structure and number in a cell LiverAlbumin Hepatocyte Principal protein produced by the liver; indicatesfunctioning of maturing and fully differentiated hepatocytes B-1integrin Hepatocyte Cell-adhesion molecule important in cell- cellinteractions; marker expressed during development of liver NervousSystem CD133 Neural stem cell, Cell-surface protein that identifiesneural HSC stem cells, which give rise to neurons and glial cells Glialfibrillary acidic Astrocyte Protein specifically produced by astrocyteprotein (GFAP) Microtubule-associated Neuron Dendrite-specific MAP;protein found protein-2 specifically in dendritic branching of neuron(MAP-2) Myelin basic protein Oligodendrocyte Protein produced by mature(MPB) oligodendrocytes; located in the myelin sheath surroundingneuronal structures Nestin Neural progenitor Intermediate filamentstructural protein expressed in primitive neural tissue Neural tubulinNeuron Important structural protein for neuron; identifiesdifferentiated neuron Neurofilament Neuron Important structural proteinfor neuron; (NF) identifies differentiated neuron Neurosphere Embryoidbody Cluster of primitive neural cells in culture of (EB), ESdifferentiating ES cells; indicates presence of early neurons and gliaNoggin Neuron A neuron-specific gene expressed during the development ofneurons O4 Oligodendrocyte Cell-surface marker on immature, developingoligodendrocyte O1 Oligodendrocyte Cell-surface marker thatcharacterizes mature oligodendrocyte Synaptophysin Neuron Neuronalprotein located in synapses; indicates connections between neurons TauNeuron Type of MAP; helps maintain structure of the axon PancreasCytokeratin 19 Pancreatic CK19 identifies specific pancreatic (CK19)epithelium epithelial cells that are progenitors for islet cells andductal cells Glucagon Pancreatic islet Expressed by alpha-islet cell ofpancreas Insulin Pancreatic islet Expressed by beta-islet cell ofpancreas Insulin-promoting factor-1 Pancreatic islet Transcriptionfactor expressed by beta-islet (PDX-1) cell of pancreas NestinPancreatic Structural filament protein indicative of progenitorprogenitor cell lines including pancreatic Pancreatic polypeptidePancreatic islet Expressed by gamma-islet cell of pancreas SomatostatinPancreatic islet Expressed by delta-islet cell of pancreas PluripotentStem Cells Alkaline phosphatase Embryonic stem Elevated expression ofthis enzyme is (ES), embryonal associated with undifferentiatedpluripotent carcinoma (EC) stem cell (PSC) Alpha-fetoprotein EndodermProtein expressed during development of (AFP) primitive endoderm;reflects endodermal differentiation Bone morphogenetic Mesoderm Growthand differentiation factor expressed protein-4 during early mesodermformation and differentiation Brachyury Mesoderm Transcription factorimportant in the earliest phases of mesoderm formation anddifferentiation; used as the earliest indicator of mesoderm formationCluster designation 30 ES, EC Surface receptor molecule found (CD30)specifically on PSC Cripto ES, Gene for growth factor expressed by ES(TDGF-1) cardiomyocyte cells, primitive ectoderm, and developingcardiomyocyte GATA-4 gene Endoderm Expression increases as ESdifferentiates into endoderm GCTM-2 ES, EC Antibody to a specificextracellular-matrix molecule that is synthesized by undifferentiatedPSCs Genesis ES, EC Transcription factor uniquely expressed by ES cellseither in or during the undifferentiated state of PSCs Germ cell nuclearfactor ES, EC Transcription factor expressed by PSCs Hepatocyte Nuclearfactor-4 Endoderm Transcription factor expressed early in (HNF-4)endoderm formation Nestin Ectoderm, neural Intermediate filaments withincells; and pancreatic characteristic of primitive neuroectodermprogenitor formation Neuronal cell-adhesion Ectoderm Cell-surfacemolecule that promotes cell- molecule cell interaction; indicatesprimitive (N-CAM) neuroectoderm formation Oct-4 ES, EC Transcriptionfactor unique to PSCs; essential for establishment and maintenance ofundifferentiated PSCs Pax6 Ectoderm Transcription factor expressed as EScell differentiates into neuroepithelium Stage-specific embryonic ES, ECGlycoprotein specifically expressed in early antigen-3 (SSEA-3)embryonic development and by undifferentiated PSCs Stage-specificembryonic ES, EC Glycoprotein specifically expressed in early antigen-4(SSEA-4) embryonic development and by undifferentiated PSCs Stem cellfactor ES, EC, HSC, Membrane protein that enhances (SCF or c-Kit ligand)MSC proliferation of ES and EC cells, hematopoietic stem cell (HSCs),and mesenchymal stem cells (MSCs); binds the receptor c-Kit TelomeraseES, EC An enzyme uniquely associated with immortal cell lines; usefulfor identifying undifferentiated PSCs TRA-1-60 ES, EC Antibody to aspecific extracellular matrix molecule is synthesized byundifferentiated PSCs TRA-1-81 ES, EC Antibody to a specificextracellular matrix molecule normally synthesized by undifferentiatedPSCs Vimentin Ectoderm, neural Intermediate filaments within cells; andpancreatic characteristic of primitive neuroectoderm progenitorformation Skeletal Muscle/Cardiac/Smooth Muscle MyoD and Pax7 Myoblast,Transcription factors that direct myocyte differentiation of myoblastsinto mature myocytes Myogenin and MR4 Skeletal myocyte Secondarytranscription factors required for differentiation of myoblasts frommuscle stem cells Myosin heavy chain Cardiomyocyte A component ofstructural and contractile protein found in cardiomyocyte Myosin lightchain Skeletal myocyte A component of structural and contractile proteinfound in skeletal myocyte

Skin provides yet another potential system for the compositions andmethods described herein. Skin stem cell fate is controlled primarilythrough the well-defined transcription factor cascade ofβ-catenin-Lef1/Tcf cascade. Merrill et al. Genes Dev 2001, 15:1688-1705.As described herein, ZFPs can be used to modulate the expression ofLef1/Tcf; alternatively or in addition, expression of specific Lef1/Tcftarget genes can be modulated.

Regulation of genes involved in hematopoietic stem cells is anotherexemplary area in which ZFPs can be used. Recently, a full-scalegenome-wide expression profile of the transcriptional program ofhematopoiesis has been conducted, yielding a large amount of data(http://stemcell.princeton.edu) describing changes in gene expressionthat occur as the stem cell proceeds down the various hematopoieticlineages. ZFPs can be used to control key regulatory genes identified inthis analysis, to evoke particular transcriptional and/or phenotypicresponses. Table 2 shows exemplary markers that have been identified inhematopoietic lineages.

TABLE 2 Markers of cell type Marker Synonyms Specificity CD 1Thymocytes, Langerhans histocytes CD 2 T and NK cells CD 3 Allthymocytes, T and NK cells CD 4 Helper T cells CD 5 All T cells, some Bcells CD 7 All T cells, some myeloid cells CD 8 Cytotoxic T cells CD 10CALLA: common Early precursor and pre-B cells acute lymphocytic leukemiaantigen CD 13 Granulocytes, monocytes CD 14 Monocytes CD 15 Leu M2 Allgranulocytes, Reed Sternberg cells CD 16 NK cells and granulocytes CD 19preB, B cells, but not plasma cells CD 20 L26 preB, but not plasma cellsCD21 EBV-R Mature B and follicular dendritic cells CD 22 Mature B CD 23Activated marrow B CD 30 Ki-I Activation marker for B, T, and monocytesCD 33 Myeloid progenitor and monocytes CD 34 Early pluripotentprogenitor cell CD 45 LCA, leukocyte All leukocytes common antigen CD 61platelet glycophorin Associated with M7 AML S100 Interdigitatingdendritic cells of the lymph node paracortex. EMA epithelial markerEpithelial cells antigen TdT T and B lymphocytes, lost before maturity

Modulation of Cellular Differentiation Using Zinc Finger Proteins

The present disclosure relates to the use of one or more engineered ZFPsto modify stem cells, for example, by creating stem cell populationsfrom specialized cells using ZFPs to modulate expression of genes thataffect dedifferentiation; by propagating stem cell populations in vivoor in vitro using ZFPs to modulate expression of genes that affectself-renewal of stem cells; or by directing a stem cell into a desiredphenotype using ZFPs to modulate expression of genes involved indifferentiation into a specialized phenotype.

Targeted control of stem cell differentiation using ZFP-TFs allows anumber of further goals to be achieved, including, but not limited to,the generation of pure “bone-marrow type” precursors of B and T cellsthat can be amplified as desired; the generation of immunoglobulin and Tcell receptor gene rearrangements to create diversity; the capacity foraffinity maturation and class-switching; the creation a suitable sourceof antigen presenting cells; the production and amplification ofcytotoxic T cells; and/or the creation of rapid and reliable individualdonor systems of different MHC haplotypes.

Dedifferentiation and Propagation of Stem Cells

Adult stem cells have been identified in brain, bone marrow, peripheralblood, blood vessels, skeletal muscle, epithelial skin and GI tractcells, cornea, dental pulp of the tooth, retina, liver, and pancreas.However, these cells are rare and often difficult to identify, isolateand purify. Further, although these cells propagate in vivo for longperiods of time, they do not survive well in culture.

Thus, researchers face many technical challenges in isolating andpropagating stem cells. These challenges include: the rarity of adultstem cells among other, differentiated cells, difficulties in isolatingand identifying the cells (e.g. by the markers they express), ethicalconsiderations regarding the use of embryonic stem cells, anddifficulties in growing stem cells in culture. Accordingly, the use ofadult stem cells in cell-replacement strategies is currently limited bythe lack of sufficient numbers of cells.

The ability of specialized cells to dedifferentiate and the ability ofstem cells to self-renew in culture are undoubtedly mediated by acomplex interaction of extrinsic (e.g., cell-cell interactions, mediaand culture conditions, extracellular matrix, etc.) and intrinsic (e.g.,gene regulation and expression) signals acting on the cell. The presentdisclosure encompasses modulation of one or more components of one orboth of intrinsic or extrinsic signals. Thus, various genes can betargeted for modulation by the ZFPs in order to maintain cells in adifferentiated state and to increase the capability of these stem cellpopulations for expansion.

In particular, the present disclosure describes the use of engineeredZFPs (or polynucleotides encoding the same) for targeted modulation ofgene expression and, accordingly, for the development of in vitro and invivo systems of obtaining and propagating stem cell populations. Thus,in certain embodiments, compositions comprising ZFPs or functionalequivalents (also referred to as “dedifferentiating compositions”) areprovided to a target cell or nucleus in an amount effective to reprogramthe target cell or nucleus from a differentiated to a dedifferentiatedstate and/or to enhance the ability of cultured stem cells to survive invivo. The amount or concentration of dedifferentiating compositionnecessary to achieve the desired effect can be readily determined by oneof skill in the art in view of the teachings herein.

Thus, one or more ZFPs engineered to modulate expression of one or moregenes involved in differentiation and/or self-renewal of stem cells areintroduced into a target cell to achieve the desired result. Forinstance, one or more ZFPs that activate the expression of genesassociated with maintaining a dedifferentiated state (e.g., stem cellphenotype) can be introduced into a target cell alone or in combinationwith ZFPs that inhibit the expression of genes associated withdifferentiation. Additionally, ZFPs that modulate expression of genesinvolved in propagation of stem cell cultures can also be introduced.

In certain aspects, the modulation (e.g., activation or repression) ofexpression by the ZFP reversible. As described in detail below, ininstances in which the repression is transient, release of theinhibitory effects would then allow controllable differentiation ofthese cells into particular lineages. Accordingly, using the teachingsdescribed herein, for example regarding the selection of suitableregulatory domains, the control of differentiation can be either stableor transient. In this way, stem cell populations can be maintained andexpanded indefinitely.

Target cells include, but are not limited to, any prokaryotic,eukaryotic and Archaeal cells. Eukaryotic cells include, plant, fungal,protozoal and animal cells, including mammalian cells, primary cells andhuman cells. If the cells are differentiated, it is first necessary torevert them to an at least partially dedifferentiated phenotype.Subsequently, the cells can be maintained and propagated in the desireddedifferentiated state using the ZFP-containing compositions and methodsdesired herein. Isolated populations of stem cells (adult or embryonic)can also be obtained and the compositions and methods described hereinused to enhance propagation and survival in the dedifferentiated state.

Target cell populations include, but are not limited to, hematopoieticstem cells such as lymphoid precursor cells, Pro-B, Pre B-1 cells,myeloid precursor cells and erythroid precursor cells as well asneuronal stem cells, pancreatic stem cells, liver stem cells andepithelial stem cells. Providing compositions and methods thatfacilitate expansion of these stem cell populations provides animportant source of stem cells for diseased and/or immunocompromisedsubjects.

Differentiation

In addition to the difficulties faced by researchers in obtainingself-renewing stem cell populations and in dedifferentiating cells, ithas also proven difficult to direct stem cells to the desiredspecialized phenotype. To this end, efforts have focused primarily ondirecting differentiation by modulating culture conditions.

Some adult stem cells appear to have the capability to differentiateinto tissue other than the one from which they originated. Thiscapability is referred to as plasticity. Reports of human or mouse adultstem cells that demonstrate plasticity include: hematopoietic stem cellsthat can differentiate into skeletal muscle cells, cardiac musclescells, liver cells and the 3 major types of brain cells (neurons,oligodendrocytes and astrocytes); stromal cells (bone marrow) thatdifferentiate into cardiac muscle cells, skeletal muscle cells, fat,bone, and cartilage; and neuronal stem cells that differentiate intoblood cells and skeletal muscle cells. (See, e.g., Anderson et al.(2001) Nature Med 7:393-395; Bjornson et al. (1999) Science 283:534-537;Mezey et al. (2000) Science 290:1779-1782; Theise et al. (2000)Heptalogy 32:11-16; U.S. Pat. No. 6,258,354).

Thus, in certain embodiments, regulation of genes involved indifferentiation by zinc finger proteins is used to obtain populations ofdifferentiated cells. The populations of cells so obtained can be fullydifferentiated (i.e., terminally differentiated) or partiallydifferentiated (i.e, multipotent but lineage-restricted). For example,up-regulation of a gene that drives differentiation, or down-regulationof a gene which drives stem cell proliferation and/or self-renewal, canbe used to move a cell toward a more differentiated state. The methodsand compositions disclosed herein can thus be used to obtain one or moreselected cell lineages, and, in certain embodiments, a single selectedcell lineage, from a population of cells. For example, pluripotent cellscan be converted to multipotent cells (e.g., hematopoietic stem cellscan be converted into myeloid precursor cells or erythroid cells), orpopulations of either pluripotent or multipotent cells can be convertedto populations of terminally differentiated cells (e.g., hematopoieticstem cells or lymphoid precursor cells can be converted to populationsof T- or B-lymphocytes).

The isolation and identification of stem cells and, additionally, thecharacterization of various states of cellular differentiation, istypically accomplished by evaluating the presence of certain markermolecules, for example, cell surface markers.

Cloning

Facilitating dedifferentiation of target cells using ZFPs can also beused to increase cloning efficiency. For example, cloning of domesticand laboratory animals is typically accomplished by transplanting a cellor nucleus (usually embryonic), into an enucleated oocyte, with theexpectation that an environment which allows for the development of anormal animal has been generated. General cloning strategies andtechniques for nuclear transplantation are described for example in U.S.Pat. No. 6,011,197 and references cited therein. However, the efficiencyof this type of nuclear transplantation is low, particularly when thenucleus to be transplanted is isolated from a somatic rather than anembryonic cell. Use of the compositions and methods described hereinallows for increased efficiency of nuclear transplantation, particularlyfor somatic cell nuclei. Exposure of nuclei to compositions comprisingone or more ZFPs targeted to genes involved in the dedifferentiationprocess allows nuclei to be reprogrammed and/or dedifferentiated tovarying degrees prior to, or coincident with, their transplantation,thereby increasing cloning efficiency.

Grafting

The compositions and methods described herein also allow for novelapproaches and systems to address immune reactions of a host toallogeneic grafts. In particular, a major problem faced when allogeneicstem cells (or any type of allogeneic cell) are grafted into a hostrecipient is the high risk of rejection by the host's immune system,primarily mediated through recognition of the Major HistocompatibilityComplex (MHC) on the surface of the engrafted cells. The MHC comprisesthe HLA class I protein(s) that function as heterodimers that arecomprised of a common β subunit and variable a subunits. It has beendemonstrated that tissue grafts derived from stem cells that are devoidof HLA escape the host's immune response. See, e.g., Coffman et al. JImmunol 151, 425-35. (1993); Markmann et al. Transplantation 54, 1085-9.(1992); Koller et al. Science 248, 1227-30. (1990). Using thecompositions and methods described herein, proteins in the HLA involvedin graft rejection can be modulated to reduce the adverse reactions. Forexample, by repressing expression of the common β subunit gene (β2microglobulin) using ZFPs as described herein, HLA class I can beremoved from the cells to rapidly and reliably generate HLA class I nullstem cells from any donor, thereby reducing the need for closely matcheddonor/recipient MHC haplotypes during stem cell grafting.

Temporal Control

In certain embodiments, the ZFP is used to modulate gene expressionconditionally, for example, at a certain time after it is introducedand/or for a set period of time. For example, HoxB4 enables long-termhematopoietic stem cells (HSC) and ES cells to give rise to bothbranches of hematopoiesis (the myeloid and lymphoid lineages) but onlytransient expression of this transcription factor to a specific level isrequired to regulate stem cell fate most effectively—with continuedexpression being counterproductive. (See, e.g., Brun et al. Blood 98,66a (2001)).

One or more of the following approaches to temporal control can be used:(i) a differentiation response following delivery of a ZFP-TF proteinitself; (ii) use of a constitutive promoter operably linked to apolynucleotide encoding a ZFP-TF; (iii) use of a inducible promoter(e.g., for example, a doxycycline-regulated promoter); (iv) use of aninducible functional domain (e.g., a hormone receptor ligand-bindingdomain). In any of these embodiments, the ZFP-encoding constructs may bestably or transiently integrated into the cell's genome. (See, e.g.,Zhang et al. J Biol Chem 275, 33850-60. (2000)).

In addition, studies show that a wide variety of genes in all eukaryoticspecies are subject to “epigenetic” regulation of gene expression—i.e.,a mode of regulation that persists, and is stable, in the absence of theinitial causative stimulus, such as action by a transcription factor.See, e.g., Chadwick, D. J. & Cardew, G. (eds.) Epigenetics (John Wiley,Chichester, England, 1998); Russo, V. E. A., Martienssen, R. A. & Riggs,A. D. (eds.) Epigenetic mechanisms of gene regulation (Cold SpringHarbor Laboratory Press, Plainview, N.Y., 1996). Epigenetic regulationis particularly central to the process of cell differentiation, asdistinguished from gene expression in general. Because the activated orrepressed state of a gene is passed on epigenetically to daughter cells,the differentiated phenotype is fixed. Such a mechanism might beexploited by permanently switching on or off an endogenous gene thatregulates differentiation, for example by use of a factor (e.g., ZFP)that will bind to and specifically modify the specified genes.

Assaying Cell State

Cells can be assayed in order to determine their particular state ofdifferentiation using a variety of well-known techniques. For example,the presence or absence of cell surface markers (e.g., Table 1) can beassayed by flow cytometry techniques, antibody binding techniques,chromatography, membrane filters, and the like. Rolink et al. (1994) IntImmunology 6:1257-1264); Jankowski et al. (2001) Hum Gene Therapy12:619-628; U.S. Pat. No. 6,268,119.

An additional assay for cell state is modulation of gene expression.Assays for gene modulation (e.g., transcriptional activation and/orrepression, reporter gene activity, measurement of protein levels) arewell-known to those of skill in the art and are described, for example,in co-owned WO 00/41566.

Polynucleotide and Polypeptide Delivery

Accordingly, in one embodiment, one or more ZFPs are expressed in a cellin order to dedifferentiate the cell (e.g., a somatic cell which is tobe used as a donor of a enucleated, inactivated or purified nucleus fortransplantation into an egg), direct a cell to particular phenotypeand/or maintain and propagate a cell in the desired state ofdifferentiation. The compositions described herein, comprising one ormore specifically targeted ZFPs, can be provided to the target cell invitro or in vivo. In addition, the compositions can be provided aspolypeptides, polynucleotides or combinations thereof.

A. Delivery of Polynucleotides

In certain embodiments, the compositions are provided as one or morepolynucleotides. Further, as noted above, the ZFPs may be designed asfusions with one or more regulatory domains and, in certain embodiments,the fusion molecule is encoded by a nucleic acid. In both fusion andnon-fusion cases, the nucleic acid can be cloned into intermediatevectors for transformation into prokaryotic or eukaryotic cells forreplication and/or expression. Intermediate vectors for storage ormanipulation of the nucleic acid or production of protein can beprokaryotic vectors, (e.g., plasmids), shuttle vectors, insect vectors,or viral vectors for example. A ZFP-encoding nucleic acid can alsocloned into an expression vector, for administration to a bacterialcell, fungal cell, protozoal cell, plant cell, or animal cell,preferably a mammalian cell, more preferably a human cell.

To obtain expression of a cloned nucleic acid, it is typically subclonedinto an expression vector that contains a promoter to directtranscription. Suitable bacterial and eukaryotic promoters are wellknown in the art and described, e.g., in Sambrook et al., supra; Ausubelet al., supra; and Kriegler, Gene Transfer and Expression: A LaboratoryManual (1990). Bacterial expression systems are available in, e.g., E.coli, Bacillus sp., and Salmonella. Palva et al. (1983) Gene 22:229-235.Kits for such expression systems are commercially available. Eukaryoticexpression systems for mammalian cells, yeast, and insect cells are wellknown in the art and are also commercially available, for example, fromInvitrogen, Carlsbad, Calif. and Clontech, Palo Alto, Calif.

The promoter used to direct expression of the nucleic acid of choicedepends on the particular application. For example, a strongconstitutive promoter is typically used for expression and purification.In contrast, when a dedifferentiation protein is to be used in vivo,either a constitutive or an inducible promoter is used, depending on theparticular use of the protein. In addition, a weak promoter can be used,such as HSV TK or a promoter having similar activity. The promotertypically can also include elements that are responsive totransactivation, e.g., hypoxia response elements, Gal4 responseelements, lac repressor response element, and small molecule controlsystems such as tet-regulated systems and the RU-486 system. See, e.g.,Gossen et al. (1992) Proc. Natl. Acad. Sci USA 89:5547-5551; Oligino etal. (1998) Gene Ther. 5:491-496; Wang et al. (1997) Gene Ther.4:432-441; Neering et al. (1996) Blood 88:1147-1155; and Rendahl et al.(1998) Nat. Biotechnol. 16:757-761.

In addition to a promoter, an expression vector typically contains atranscription unit or expression cassette that contains additionalelements required for the expression of the nucleic acid in host cells,either prokaryotic or eukaryotic. A typical expression cassette thuscontains a promoter operably linked, e.g., to the nucleic acid sequence,and signals required, e.g., for efficient polyadenylation of thetranscript, transcriptional termination, ribosome binding, and/ortranslation termination. Additional elements of the cassette mayinclude, e.g., enhancers, and heterologous spliced intronic signals.

The particular expression vector used to transport the geneticinformation into the cell is selected with regard to the intended use ofthe resulting dedifferentiation polypeptide, e.g., expression in plants,animals, bacteria, fungi, protozoa etc. Standard bacterial expressionvectors include plasmids such as pBR322, pBR322-based plasmids, pSKF,pET23D, and commercially available fusion expression systems such as GSTand LacZ. Epitope tags can also be added to recombinant proteins toprovide convenient methods of isolation, for monitoring expression, andfor monitoring cellular and subcellular localization, e.g., c-myc orFLAG.

Expression vectors containing regulatory elements from eukaryoticviruses are often used in eukaryotic expression vectors, e.g., SV40vectors, papilloma virus vectors, and vectors derived from Epstein-Barrvirus. Other exemplary eukaryotic vectors include pMSG, pAV009/A+,pMTO10/A+, pMAMneo-5, baculovirus pDSVE, and any other vector allowingexpression of proteins under the direction of the SV40 early promoter,SV40 late promoter, metallothionein promoter, murine mammary tumor viruspromoter, Rous sarcoma virus promoter, polyhedrin promoter, or otherpromoters shown effective for expression in eukaryotic cells.

Some expression systems have markers for selection of stably transfectedcell lines such as thymidine kinase, hygromycin B phosphotransferase,and dihydrofolate reductase. High-yield expression systems are alsosuitable, such as baculovirus vectors in insect cells, with adedifferentiation nucleic acid sequence under the transcriptionalcontrol of the polyhedrin promoter or any other strong baculoviruspromoter.

Elements that are typically included in expression vectors also includea replicon that functions in E. coli (or in the prokaryotic host, ifother than E. coli), a selective marker, e.g., a gene encodingantibiotic resistance, to permit selection of bacteria that harborrecombinant plasmids, and unique restriction sites in nonessentialregions of the vector to allow insertion of recombinant sequences.

Standard transfection methods can be used to produce bacterial,mammalian, yeast, insect, or other cell lines that express largequantities of dedifferentiation proteins, which can be purified, ifdesired, using standard techniques. See, e.g., Colley et al. (1989) J.Biol. Chem. 264:17619-17622; and Guide to Protein Purification, inMethods in Enzymology, vol. 182 (Deutscher, ed.) 1990. Transformation ofeukaryotic and prokaryotic cells are performed according to standardtechniques. See, e.g., Morrison (1977) J. Bacteriol. 132:349-351;Clark-Curtiss et al. (1983) in Methods in Enzymology 101:347-362 (Wu etal., eds).

Any procedure for introducing foreign nucleotide sequences into hostcells can be used. These include, but are not limited to, the use ofcalcium phosphate transfection, DEAE-dextran-mediated transfection,polybrene, protoplast fusion, electroporation, lipid-mediated delivery(e.g., liposomes), microinjection, particle bombardment, introduction ofnaked DNA, plasmid vectors, viral vectors (both episomal andintegrative) and any of the other well known methods for introducingcloned genomic DNA, cDNA, synthetic DNA or other foreign geneticmaterial into a host cell (see, e.g., Sambrook et al., supra). It isonly necessary that the particular genetic engineering procedure used becapable of successfully introducing at least one gene into the host cellcapable of expressing the protein of choice.

Conventional viral and non-viral based gene transfer methods can be usedto introduce nucleic acids into mammalian cells or target tissues. Suchmethods can be used to administer nucleic acids encoding reprogrammingpolypeptides to cells in vitro. Preferably, nucleic acids areadministered for in vivo or ex vivo gene therapy uses. Non-viral vectordelivery systems include DNA plasmids, naked nucleic acid, and nucleicacid complexed with a delivery vehicle such as a liposome. Viral vectordelivery systems include DNA and RNA viruses, which have either episomalor integrated genomes after delivery to the cell. For reviews of genetherapy procedures, see, for example, Anderson (1992) Science256:808-813; Nabel et al. (1993) Trends Biotechnol. 11:211-217; Mitaniet al. (1993) Trends Biotechnol. 11:162-166; Dillon (1993) TrendsBiotechnol. 11:167-175; Miller (1992) Nature 357:455-460; Van Brunt(1988) Biotechnology 6(10):1149-1154; Vigne (1995) Restorative Neurologyand Neuroscience 8:35-36; Kremer et al. (1995) British Medical Bulletin51(1):31-44; Haddada et al., in Current Topics in Microbiology andImmunology, Doerfler and Bohm (eds), 1995; and Yu et al. (1994) GeneTherapy 1:13-26.

Methods of non-viral delivery of nucleic acids include lipofection,microinjection, ballistics, virosomes, liposomes, immunoliposomes,polycation or lipid:nucleic acid conjugates, naked DNA, artificialvirions, and agent-enhanced uptake of DNA. Lipofection is described in,e.g., U.S. Pat. Nos. 5,049,386; 4,946,787; and 4,897,355 and lipofectionreagents are sold commercially (e.g., Transfectam™ and Lipofectin™).Cationic and neutral lipids that are suitable for efficientreceptor-recognition lipofection of polynucleotides include those ofFelgner, WO 91/17424 and WO 91/16024. Nucleic acid can be delivered tocells (ex vivo administration) or to target tissues (in vivoadministration).

The preparation of lipid:nucleic acid complexes, including targetedliposomes such as immunolipid complexes, is well known to those of skillin the art. See, e.g., Crystal (1995) Science 270:404-410; Blaese et al.(1995) Cancer Gene Ther. 2:291-297; Behr et al. (1994) BioconjugateChem. 5:382-389; Remy et al. (1994) Bioconjugate Chem. 5:647-654; Gao etal. (1995) Gene Therapy 2:710-722; Ahmad et al. (1992) Cancer Res.52:4817-4820; and U.S. Pat. Nos. 4,186,183; 4,217,344; 4,235,871;4,261,975; 4,485,054; 4,501,728; 4,774,085; 4,837,028 and 4,946,787.

The use of RNA or DNA virus-based systems for the delivery of nucleicacids take advantage of highly evolved processes for targeting a virusto specific cells in the body and trafficking the viral payload to thenucleus. Viral vectors can be administered directly to patients (invivo) or they can be used to treat cells in vitro, wherein the modifiedcells are administered to patients (ex vivo). Conventional viral basedsystems for the delivery of ZFPs include retroviral, lentiviral,poxviral, adenoviral, adeno-associated viral, vesicular stomatitis viraland herpesviral vectors. Integration in the host genome is possible withcertain viral vectors, including the retrovirus, lentivirus, andadeno-associated virus gene transfer methods, often resulting in longterm expression of the inserted transgene. Additionally, hightransduction efficiencies have been observed in many different celltypes and target tissues.

The tropism of a retrovirus can be altered by incorporating foreignenvelope proteins, allowing alteration and/or expansion of the potentialtarget cell population. Lentiviral vectors are retroviral vector thatare able to transduce or infect non-dividing cells and typically producehigh viral titers. Selection of a retroviral gene transfer system wouldtherefore depend on the target tissue. Retroviral vectors have apackaging capacity of up to 6-10 kb of foreign sequence and arecomprised of cis-acting long terminal repeats (LTRs). The minimumcis-acting LTRs are sufficient for replication and packaging of thevectors, which are then used to integrate the therapeutic gene into thetarget cell to provide permanent transgene expression. Widely usedretroviral vectors include those based upon murine leukemia virus(MuLV), gibbon ape leukemia virus (GaLV), simian immunodeficiency virus(SIV), human immunodeficiency virus (HIV), and combinations thereof.Buchscher et al. (1992) J. Virol. 66:2731-2739; Johann et al. (1992) J.Virol. 66:1635-1640; Sommerfelt et al. (1990) Virol. 176:58-59; Wilsonet al. (1989) J. Virol. 63:2374-2378; Miller et al. (1991) J. Virol.65:2220-2224; and PCT/US94/05700).

Adeno-associated virus (AAV) vectors are also used to transduce cellswith target nucleic acids, e.g., in the in vitro production of nucleicacids and peptides, and for in vivo and ex vivo gene therapy procedures.See, e.g., West et al. (1987) Virology 160:38-47; U.S. Pat. No.4,797,368; WO 93/24641; Kotin (1994) Hum. Gene Ther. 5:793-801; andMuzyczka (1994) J. Clin. Invest. 94:1351. Construction of recombinantAAV vectors are described in a number of publications, including U.S.Pat. No. 5,173,414; Tratschin et al. (1985) Mol. Cell. Biol.5:3251-3260; Tratschin, et al. (1984) Mol. Cell. Biol. 4:2072-2081;Hermonat et al. (1984) Proc. Natl. Acad. Sci. USA 81:6466-6470; andSamulski et al. (1989) J. Virol. 63:3822-3828.

Recombinant adeno-associated virus vectors based on the defective andnonpathogenic parvovirus adeno-associated virus type 2 (AAV-2) are apromising gene delivery system. Exemplary AAV vectors are derived from aplasmid containing the AAV 145 bp inverted terminal repeats flanking atransgene expression cassette. Efficient gene transfer and stabletransgene delivery due to integration into the genomes of the transducedcell are key features for this vector system. Wagner et al. (1998)Lancet 3510(9117):1702-3; and Kearns et al. (1996) Gene Ther. 9:748-55.

pLASN and MFG-S are examples are retroviral vectors that have been usedin clinical trials. Dunbar et al. (1995) Blood 85:3048-305; Kohn et al.(1995) Nature Med. 1:1017-102; Malech et al. (1997) Proc. Natl. Acad.Sci. USA 94:12133-12138. PA317/pLASN was the first therapeutic vectorused in a gene therapy trial. (Blaese et al. (1995) Science 270:475-480.Transduction efficiencies of 50% or greater have been observed for MFG-Spackaged vectors. Ellem et al. (1997) Immunol Immunother. 44(1):10-20;Dranoff et al. (1997) Hum. Gene Ther. 1:111-2.

In applications for which transient expression is preferred,adenoviral-based systems are useful. Adenoviral based vectors arecapable of very high transduction efficiency in many cell types and arecapable of infecting, and hence delivering nucleic acid to, bothdividing and non-dividing cells. With such vectors, high titers andlevels of expression have been obtained. Adenovirus vectors can beproduced in large quantities in a relatively simple system.

Replication-deficient recombinant adenoviral (Ad) can be produced athigh titer and they readily infect a number of different cell types.Most adenovirus vectors are engineered such that a transgene replacesthe Ad E1a, E1b, and/or E3 genes; the replication defector vector ispropagated in human 293 cells that supply the required E1 functions intrans. Ad vectors can transduce multiple types of tissues in vivo,including non-dividing, differentiated cells such as those found in theliver, kidney and muscle. Conventional Ad vectors have a large carryingcapacity for inserted DNA. An example of the use of an Ad vector in aclinical trial involved polynucleotide therapy for antitumorimmunization with intramuscular injection. Sterman et al. (1998) Hum.Gene Ther. 7:1083-1089. Additional examples of the use of adenovirusvectors for gene transfer in clinical trials include Rosenecker et al.(1996) Infection 24:5-10; Sterman et al., supra; Welsh et al. (1995)Hum. Gene Ther. 2:205-218; Alvarez et al. (1997) Hum. Gene Ther.5:597-613; and Topf et al. (1998) Gene Ther. 5:507-513.

Packaging cells are used to form virus particles that are capable ofinfecting a host cell. Such cells include 293 cells, which packageadenovirus, and Ψ2 cells or PA317 cells, which package retroviruses.Viral vectors used in gene therapy are usually generated by a producercell line that packages a nucleic acid vector into a viral particle. Thevectors typically contain the minimal viral sequences required forpackaging and subsequent integration into a host, other viral sequencesbeing replaced by an expression cassette for the protein to beexpressed. Missing viral functions are supplied in trans, if necessary,by the packaging cell line. For example, AAV vectors used in genetherapy typically only possess ITR sequences from the AAV genome, whichare required for packaging and integration into the host genome. ViralDNA is packaged in a cell line, which contains a helper plasmid encodingthe other AAV genes, namely rep and cap, but lacking ITR sequences. Thecell line is also infected with adenovirus as a helper. The helper viruspromotes replication of the AAV vector and expression of AAV genes fromthe helper plasmid. The helper plasmid is not packaged in significantamounts due to a lack of ITR sequences. Contamination with adenoviruscan be reduced by, e.g., heat treatment, which preferentiallyinactivates adenoviruses.

In many gene therapy applications, it is desirable that the gene therapyvector be delivered with a high degree of specificity to a particulartissue type. A viral vector can be modified to have specificity for agiven cell type by expressing a ligand as a fusion protein with a viralcoat protein on the outer surface of the virus. The ligand is chosen tohave affinity for a receptor known to be present on the cell type ofinterest. For example, Han et al. (1995) Proc. Natl. Acad. Sci. USA92:9747-9751 reported that Moloney murine leukemia virus can be modifiedto express human heregulin fused to gp70, and the recombinant virusinfects certain human breast cancer cells expressing human epidermalgrowth factor receptor. This principle can be extended to other pairs ofvirus expressing a ligand fusion protein and target cell expressing areceptor. For example, filamentous phage can be engineered to displayantibody fragments (e.g., Fab or F_(v)) having specific binding affinityfor virtually any chosen cellular receptor. Although the abovedescription applies primarily to viral vectors, the same principles canbe applied to non-viral vectors. Such vectors can be engineered tocontain specific uptake sequences thought to favor uptake by specifictarget cells.

Gene therapy vectors can be delivered in vivo by administration to anindividual patient, typically by systemic administration (e.g.,intravenous, intraperitoneal, intramuscular, subdermal, or intracranialinfusion) or topical application, as described infra. Alternatively,vectors can be delivered to cells ex vivo, such as cells explanted froman individual patient (e.g., lymphocytes, bone marrow aspirates, tissuebiopsy) or universal donor hematopoietic stem cells, followed byreimplantation of the cells into a patient, usually after selection forcells which have incorporated the vector.

Ex vivo cell transfection for diagnostics, research, or for gene therapy(e.g., via re-infusion of the transfected cells into the host organism)is well known to those of skill in the art. In a preferred embodiment,cells are isolated from the subject organism, transfected with a nucleicacid (gene or cDNA), and re-infused back into the subject organism(e.g., patient). Various cell types suitable for ex vivo transfectionare well known to those of skill in the art. See, e.g., Freshney et al.,Culture of Animal Cells, A Manual of Basic Technique, 3rd ed., 1994, andreferences cited therein, for a discussion of isolation and culture ofcells from patients.

In one embodiment, hematopoietic stem cells are used in ex vivoprocedures for cell transfection and gene therapy. The advantage tousing stem cells is that they can be differentiated into other celltypes in vitro, or can be introduced into a mammal (such as the donor ofthe cells) where they will engraft in the bone marrow. Methods fordifferentiating CD34+ stem cells in vitro into clinically importantimmune cell types using cytokines such a GM-CSF, IFN-γ and TNF-α areknown. Inaba et al. (1992) J. Exp. Med. 176:1693-1702.

Stem cells are isolated for transduction and differentiation using knownmethods. For example, stem cells are isolated from bone marrow cells bypanning the bone marrow cells with antibodies which bind unwanted cells,such as CD4+ and CD8+(T cells), CD45+ (panB cells), GR-1 (granulocytes),and Tad (differentiated antigen presenting cells). See Inaba et al.,supra.

Vectors (e.g., retroviruses, adenoviruses, liposomes, etc.) containingtherapeutic nucleic acids can be also administered directly to theorganism for transduction of cells in vivo. Alternatively, naked DNA canbe administered. Administration is by any of the routes normally usedfor introducing a molecule into ultimate contact with blood or tissuecells. Suitable methods of administering such nucleic acids areavailable and well known to those of skill in the art, and, althoughmore than one route can be used to administer a particular composition,a particular route can often provide a more immediate and more effectivereaction than another route.

Pharmaceutically acceptable carriers are determined in part by theparticular composition being administered, as well as by the particularmethod used to administer the composition. Accordingly, there is a widevariety of suitable formulations of pharmaceutical compositions, asdescribed below. See, e.g., Remington's Pharmaceutical Sciences, 17thed., 1989.

B. Delivery of Polypeptides

In other embodiments, for example in certain in vitro situations, thetarget cells are cultured in a medium containing one or more targetedZFPs.

An important factor in the administration of polypeptide compounds isensuring that the polypeptide has the ability to traverse the plasmamembrane of a cell, or the membrane of an intra-cellular compartmentsuch as the nucleus. Cellular membranes are composed of lipid-proteinbilayers that are freely permeable to small, nonionic lipophiliccompounds and are inherently impermeable to polar compounds,macromolecules, and therapeutic or diagnostic agents. However, proteins,lipids and other compounds, which have the ability to translocatepolypeptides across a cell membrane, have been described.

For example, “membrane translocation polypeptides” have amphiphilic orhydrophobic amino acid subsequences that have the ability to act asmembrane-translocating carriers. In one embodiment, homeodomain proteinshave the ability to translocate across cell membranes. The shortestinternalizable peptide of a homeodomain protein, Antennapedia, was foundto be the third helix of the protein, from amino acid position 43 to 58.Prochiantz (1996) Curr. Opin. Neurobiol. 6:629-634. Another subsequence,the h (hydrophobic) domain of signal peptides, was found to have similarcell membrane translocation characteristics. Lin et al. (1995) J. Biol.Chem. 270:14255-14258.

Examples of peptide sequences which can facilitate protein uptake intocells include, but are not limited to: an 11 amino acid peptide of thetat protein of HIV; a 20 residue peptide sequence which corresponds toamino acids 84-103 of the p16 protein (see Fahraeus et al. (1996) Curr.Biol. 6:84); the third helix of the 60-amino acid long homeodomain ofAntennapedia (Derossi et al. (1994) J. Biol. Chem. 269:10444); the hregion of a signal peptide, such as the Kaposi fibroblast growth factor(K-FGF) h region (Lin et al., supra); and the VP22 translocation domainfrom HSV (Elliot et al. (1997) Cell 88:223-233). Other suitable chemicalmoieties that provide enhanced cellular uptake can also be linked,either covalently or non-covalently, to the ZFP or ZFP-containing fusionmolecules.

Toxin molecules also have the ability to transport polypeptides acrosscell membranes. Often, such molecules (called “binary toxins”) arecomposed of at least two parts: a translocation or binding domain and aseparate toxin domain. Typically, the translocation domain, which canoptionally be a polypeptide, binds to a cellular receptor, facilitatingtransport of the toxin into the cell. Several bacterial toxins,including Clostridium perfringens iota toxin, diphtheria toxin (DT),Pseudomonas exotoxin A (PE), pertussis toxin (PT), Bacillus anthracistoxin, and pertussis adenylate cyclase (CYA), have been used to deliverpeptides to the cell cytosol as internal or amino-terminal fusions.Arora et al. (1993) J. Biol. Chem. 268:3334-3341; Perelle et al. (1993)Infect. Immun. 61:5147-5156; Stenmark et al. (1991) J. Cell Biol.113:1025-1032; Donnelly et al. (1993) Proc. Natl. Acad. Sci. USA90:3530-3534; Carbonetti et al. (1995) Abstr. Annu. Meet. Am. Soc.Microbiol. 95:295; Sebo et al. (1995) Infect. Immun. 63:3851-3857;Klimpel et al. (1992) Proc. Natl. Acad. Sci. USA. 89:10277-10281; andNovak et al. (1992) J. Biol. Chem. 267:17186-17193.

Such subsequences can be used to translocate polypeptides, including thepolypeptides as disclosed herein, across a cell membrane. This isaccomplished, for example, by derivatizing the fusion polypeptide withone of these translocation sequences, or by forming an additional fusionof the translocation sequence with the fusion polypeptide. Optionally, alinker can be used to link the fusion polypeptide and the translocationsequence. Any suitable linker can be used, e.g., a peptide linker.

A suitable polypeptide can also be introduced into an animal cell,preferably a mammalian cell, via liposomes and liposome derivatives suchas immunoliposomes. The term “liposome” refers to vesicles comprised ofone or more concentrically ordered lipid bilayers, which encapsulate anaqueous phase. The aqueous phase typically contains the compound to bedelivered to the cell.

The liposome fuses with the plasma membrane, thereby releasing thecompound into the cytosol. Alternatively, the liposome is phagocytosedor taken up by the cell in a transport vesicle. Once in the endosome orphagosome, the liposome is either degraded or it fuses with the membraneof the transport vesicle and releases its contents.

In current methods of drug delivery via liposomes, the liposomeultimately becomes permeable and releases the encapsulated compound atthe target tissue or cell. For systemic or tissue specific delivery,this can be accomplished, for example, in a passive manner wherein theliposome bilayer is degraded over time through the action of variousagents in the body. Alternatively, active drug release involves using anagent to induce a permeability change in the liposome vesicle. Liposomemembranes can be constructed so that they become destabilized when theenvironment becomes acidic near the liposome membrane. See, e.g., Proc.Natl. Acad. Sci. USA 84:7851 (1987); Biochemistry 28:908 (1989). Whenliposomes are endocytosed by a target cell, for example, they becomedestabilized and release their contents. This destabilization is termedfusogenesis. Dioleoylphosphatidylethanolamine (DOPE) is the basis ofmany “fusogenic” systems.

For use with the methods and compositions disclosed herein, liposomestypically comprise a fusion polypeptide as disclosed herein, a lipidcomponent, e.g., a neutral and/or cationic lipid, and optionally includea receptor-recognition molecule such as an antibody that binds to apredetermined cell surface receptor or ligand (e.g., an antigen). Avariety of methods are available for preparing liposomes as describedin, e.g.; U.S. Pat. Nos. 4,186,183; 4,217,344; 4,235,871; 4,261,975;4,485,054; 4,501,728; 4,774,085; 4,837,028; 4,235,871; 4,261,975;4,485,054; 4,501,728; 4,774,085; 4,837,028; 4,946,787; PCT PublicationNo. WO 91/17424; Szoka et al. (1980) Ann. Rev. Biophys. Bioeng. 9:467;Deamer et al. (1976) Biochim. Biophys. Acta 443:629-634; Fraley, et al.(1979) Proc. Natl. Acad. Sci. USA 76:3348-3352; Hope et al. (1985)Biochim. Biophys. Acta 812:55-65; Mayer et al. (1986) Biochim. Biophys.Acta 858:161-168; Williams et al. (1988) Proc. Natl. Acad. Sci. USA85:242-246; Liposomes, Ostro (ed.), 1983, Chapter 1); Hope et al. (1986)Chem. Phys. Lip. 40:89; Gregoriadis, Liposome Technology (1984) andLasic, Liposomes: from Physics to Applications (1993). Suitable methodsinclude, for example, sonication, extrusion, highpressure/homogenization, microfluidization, detergent dialysis,calcium-induced fusion of small liposome vesicles and ether-fusionmethods, all of which are well known in the art.

In certain embodiments, it may be desirable to target a liposome usingtargeting moieties that are specific to a particular cell type, tissue,and the like. Targeting of liposomes using a variety of targetingmoieties (e.g., ligands, receptors, and monoclonal antibodies) has beenpreviously described. See, e.g., U.S. Pat. Nos. 4,957,773 and 4,603,044.

Examples of targeting moieties include monoclonal antibodies specific toantigens associated with neoplasms, such as prostate cancer specificantigen and MAGE. Tumors can also be diagnosed by detecting geneproducts resulting from the activation or over-expression of oncogenes,such as ras or c-erbB2. In addition, many tumors express antigensnormally expressed by fetal tissue, such as the alphafetoprotein (AFP)and carcinoembryonic antigen (CEA). Sites of viral infection can bediagnosed using various viral antigens such as hepatitis B core andsurface antigens (HBVc, HBVs) hepatitis C antigens, Epstein-Barr virusantigens, human immunodeficiency type-1 virus (HIV-1) and papillomavirus antigens. Inflammation can be detected using moleculesspecifically recognized by surface molecules which are expressed atsites of inflammation such as integrins (e.g., VCAM-1), selectinreceptors (e.g., ELAM-1) and the like.

Standard methods for coupling targeting agents to liposomes are used.These methods generally involve the incorporation into liposomes oflipid components, e.g., phosphatidylethanolamine, which can be activatedfor attachment of targeting agents, or incorporation of derivatizedlipophilic compounds, such as lipid derivatized bleomycin. Antibodytargeted liposomes can be constructed using, for instance, liposomeswhich incorporate protein A. See Renneisen et al. (1990) J. Biol. Chem.265:16337-16342 and Leonetti et al. (1990) Proc. Natl. Acad. Sci. USA87:2448-2451.

Pharmaceutical Compositions and Administration

ZFPs as disclosed herein, and expression vectors encoding thesepolypeptides, can be used in conjunction with various methods tofacilitate treatment of various disease states, congenital conditions ordegenerative illnesses. In such applications, targeted ZFP polypeptidesor polynucleotides encoding these ZFPs can be administered directly to apatient, e.g., to facilitate the modulation of gene expression involvedin differentiation and replacement of specific stem cell types, forexample, in cancer, ischemia, diabetic retinopathy, maculardegeneration, rheumatoid arthritis, psoriasis, HIV infection, sicklecell anemia, Alzheimer's disease, muscular dystrophy, neurodegenerativediseases, vascular disease, cystic fibrosis, stroke, and the like.

Administration of therapeutically effective amounts of one or more ZFPsor a nucleic acid encoding such ZFPs is by any of the routes normallyused for introducing polypeptides or nucleic acids into ultimate contactwith the tissue to be treated. The polypeptides or nucleic acids areadministered in any suitable manner, preferably with pharmaceuticallyacceptable carriers. Suitable methods of administering such modulatorsare available and well known to those of skill in the art, and, althoughmore than one route can be used to administer a particular composition,a particular route can often provide a more immediate and more effectivereaction than another route.

Pharmaceutically acceptable carriers are determined in part by theparticular composition being administered, as well as by the particularmethod used to administer the composition. Accordingly, there are a widevariety of suitable formulations of pharmaceutical compositions. See,e.g., Remington's Pharmaceutical Sciences, 17^(th) ed. 1985.

ZFPs polypeptides or nucleic acids, alone or in combination with othersuitable components, can be made into aerosol formulations (e.g., theycan be “nebulized”) to be administered via inhalation. Aerosolformulations can be placed into pressurized acceptable propellants, suchas dichlorodifluoromethane, propane, nitrogen, and the like.

Formulations suitable for parenteral administration, such as, forexample, by intravenous, intramuscular, intradermal, and subcutaneousroutes, include aqueous and non-aqueous, isotonic sterile injectionsolutions, which can contain antioxidants, buffers, bacteriostats, andsolutes that render the formulation isotonic with the blood of theintended recipient, and aqueous and non-aqueous sterile suspensions thatcan include suspending agents, solubilizers, thickening agents,stabilizers, and preservatives. Compositions can be administered, forexample, by intravenous infusion, orally, topically, intraperitoneally,intravesically or intrathecally. The formulations of compounds can bepresented in unit-dose or multi-dose sealed containers, such as ampoulesand vials. Injection solutions and suspensions can be prepared fromsterile powders, granules, and tablets of the kind known to those ofskill in the art.

Applications

The compositions and methods disclosed herein can be used to facilitatea number of processes involved in development and dedifferentiation.These processes include, but are not limited to, dedifferentiation ordifferentiation of a target cell, cloning, creation of cell lineages,immortalization of cells, replication, recombination, repair and/orintegration. Accordingly, the methods and compositions disclosed hereincan be used to affect any of these processes, as well as any otherdevelopmental process which can be influenced by modulation of geneexpression, including epigenetic modulation.

In one embodiment, the compositions and methods disclosed herein areused to provide transplant tissue or cells that are not subject toimmune rejection by the recipient. See, e.g., See, e.g., Coffman et al.J. Immunol 151, 425-35. (1993); Markmann et al. Transplantation 54,1085-9. (1992); Koller et al. Science 248, 1227-30. (1990); Gurdon etal. Nature 402(6763):743-6 (1999). Obtaining or generating adedifferentiated stem cell and directing differentiation into aparticular cell type using one or more ZFPs can lead to production oftissue suitable for transplant into the individual in need thereof. Incertain embodiments, the stem cell is obtained from the transplantrecipient, and, accordingly, it will not stimulate an immune response,as would tissue from an unrelated donor. Such transplants can constitutesolid organ transplants (e.g., heart, liver, kidney) or cell transplantsfor the treatment of various malignancies such as, for example,leukemias and lymphomas. The stem cells can be differentiated using ZFPsin vitro or, alternatively, in vivo. Such transplants can also be usedin the treatment of, for example, neurological disorders, diabetes andthe like.

EXAMPLES

The following examples are presented as illustrative of, but notlimiting, the claimed subject matter.

Example 1: OCT4 Function in Stem Cells

The OCT 4 transcription factor (also known as OCT3/4) is expressed ingerm cells and in totipotent embryonic stem cells (ES cells). It isinvolved in the regulation of a number of genes, either directly orindirectly. Expression of OCT4, together with expression of the Stat3gene product, is correlated with maintenance of totipotency andself-renewal (e.g., proliferation) of stem cells. During embryonicdevelopment, down-regulation of OCT4 expression results indifferentiation.

Recent studies in which its expression was modulated in ES cells haveshown that levels of OCT4 expression ranging between 50 and 150% ofnormal levels are sufficient for self-renewal of the stem cellpopulation and maintenance of totipotency. Lower levels of OCT4expression (50% or less of normal) result in differentiation intotrophectoderm, while OCT4 levels above 150% of normal result indifferentiation into endoderm and mesoderm. See, Niwa et al. (2000)Nature Genetics 24:372-376.

Changes in levels of OCT4 expression are correlated with changes inexpression of a number of other genes, indicating that expression ofthese genes is likely to be regulated, either directly or indirectly, byOCT4. In particular, increase in OCT4 expression, from an integratedcDNA, in ES cells resulted in an increase in expression of the Otx1gene. Decreased levels of OCT4 resulted in repression of Otx1 andactivation of Hand1, a transcription factor involved in trophoblastdifferentiation. Niwa et al. (2000) Nature Genetics 24:372-376.

Example 2: Design of ZFPs that Bind the OCT4 Gene

A ZFP binding domain, targeted to a sequence approximately 130nucleotides upstream of the transcriptional start site of the mouse OCT4 gene, was designed using methods for the design and synthesis of zincfinger proteins able to bind to preselected sites disclosed in co-ownedU.S. Pat. No. 6,453,242; WO 00/41566 and PCT/US01/43568. The targetsequence and the amino acid sequences of the recognition regions of thezinc fingers of this protein is given in Table 3.

TABLE 3  Designed zinc finger protein binding domains binding  F1  F2 F3  ZFP# target site sequence* sequence* sequence* 1547 OCT4 GAGGTKGGGRSDHLAR TSGSLTR RSDNLAR (SEQ ID (SEQ ID (SEQ ID (SEQ ID NO: 1) NO: 2)NO: 3) NO: 4) *The amino acid sequences shown are those of amino acids−1 through +6 (with respect to the start of the alpha-helical portion ofthe zinc finger) and are given in the one-letter code

Constructs were generated in which sequences encoding the ZFP bindingdomains shown in Table 3 were fused either to sequences encoding a VP16transcriptional activation domain (construct named v-1547) or tosequences encoding a KOX-1 repression domain (construct named x-1547),using methods disclosed in co-owned U.S. Pat. No. 6,453,242 and co-ownedWO 00/41566. These constructs were separately transfected into mouse EScells, and their effects on expression of the OCT 4 gene weredetermined.

Example 3: Regulation of the OCT4 Gene in Mouse Embryonic Stem CellsUsing Engineered Zinc Finger Proteins

Mouse embryonic stem cell line ES-D3 was obtained from the American TypeCulture Collection (ATCC, Manassas, Va.). Cells were propagated ongelatin coated dishes at 37° C. in Knockout D-MEM medium (Gibco-BRL)supplemented with 10% FBS, 2 mM L-glutamine and 10 ng/ml murine leukemiainhibitory factor (LIF).

For transfection, cells were plated in 12-well plates at a density of2×10⁵ cells per well one day before transfection. For each well 1.7 μgDNA (v-1547 or x-1547 or GFP, a negative control) was diluted in 180 μlserum-free OPTI-MEM I medium, mixed with LipofectAMINE 2000 (4 μldiluted in 180 μl OPTI-MEM I), and incubated for 20 minutes at roomtemperature. Cells were rinsed with serum-free medium, and thetransfection mixture was introduced into the well. After 4-5 h, thetransfection mixture was replaced with regular growth medium.

At 48 h after transfection, total cellular RNA was isolated using the“High Pure RNA Isolation Kit” (Roche Diagnostics Corporation,Indianapolis, Ind.) and was analyzed for OCT4 mRNA levels by real-timePCR (TaqMan®, Roche), using an ABI PRISM 7700 Sequence Detector (AppliedBiosystems, Foster City, Calif.). Glyceraldehyde-3-phosphatedehydrogenase (GAPDH) mRNA levels were also measured and used as anormalization standard. Primers and probes used for mRNA analysis aregiven in Table 4.

TABLE 4  Probe and primer sequences for RNA analysis SEQ ID GeneOligonucleotide SEQUENCE NO OCT4 Forward primer CTCACCCTGGGCGTTCTCT 5Reverse primer AGGCCTCGAAGCGACAGA 6 Probe TGGAAAGGTGTTCAGCCAGACC 7 ACCOTX1 Forward primer ATCAACCTGCCAGAGTCCAGAGT 8 Reverse primerCCGGGTTTTCGTTCCATTC 9 Probe AGTGCCGCCAGCAGCAGCAGA 10 Hand1Forward primer GCCAAGGATGCACAAGCA 11 Reverse primer GGGCTGCTGAGGCAACTC12 Probe CTTTTCCGCTTGCTTTCGCGACC 13 HOXB4 Forward primerGGAACAGCGAGCACCGAA 14 Reverse primer CCTTTCTATAAATAAGGCTTCCC 15 TACCProbe CCCCGGGCTTGAGCCCAGAA 16 GAPDH Forward primer CCCATGTTTGTGATGGGTGTG17 Reverse primer TGGCATGGACTGTGGTCATGA 18 Probe ATCCTGCACCACCAACTGCTTA19 GC

Results are shown in FIGS. 1 and 2. Introduction of the v-1547construct, encoding a fusion between a ZFP targeted to OCT4 and the VP16activation domain, resulted in an approximately two-fold increase inOCT4 mRNA levels, compared to cells transfected with a GFP-encodingvector (FIG. 1). Introduction of the x-1547 construct, encoding a fusionbetween an OCT4-targeted ZFP and the KOX-1 repression domain, resultedin a decrease in OCT4 mRNA levels, compared to cells transfected with aGFP-encoding vector (FIG. 2). These results demonstrate that it ispossible to use engineered zinc finger proteins to regulate a keydevelopmental control gene in stem cells.

Example 4: Effect of ZFP-Mediated Regulation of the OCT4 Gene onExpression of Downstream Genes

As stated previously (see Example 1), upregulation of OCT4 in stem cellshas been shown to result in upregulation of the Otx1 gene; whiledownregulation of OCT4 results in repression of Otx1 and activation ofHand1 expression. To determine whether ZFP-mediated regulation of OCT4has the same effect on downstream genes, RNA from cells that had beentransfected with v-1547 or with x-1547 (e.g., the same RNA samples thatwere analyzed in Example 3) was assayed for Otx1 and Hand1 mRNA levels,normalized to GAPDH mRNA.

The results are shown in FIGS. 3, 4 and 5. FIG. 3 shows that, in cellsin which OCT4 mRNA levels had been increased by the v-1547 ZFP, Otx1mRNA levels were also increased, as previously observed. FIGS. 4 and 5show analysis of RNA from cells in which OCT4 expression wasdownregulated by the x-1547 ZFP. FIG. 4 shows that Otx1 mRNA levels werealso downregulated, and FIG. 5 shows that Hand1 mRNA levels increasedfollowing repression of OCT4 expression. Thus, these results demonstratethat modulation of OCT4 expression in stem cells with an engineered ZFPresults in the expected co-regulation of downstream genes.

Example 5: Design of ZFPs that Bind the HOXB4 Gene

The HOXB4 gene is a homeobox transcription factor primarily expressed inthe most primitive subpopulations of hematopoietic cells, and has beenshown to be important for their proliferation. See, e.g., Helgason etal. (1996) Blood 87:2740-2749; Antonchuk et al. (2002) Cell 109:39-45.

A ZFP binding domain, targeted to four sites within the first exon ofthe HOXB4 gene, was designed using methods for the design and synthesisof zinc finger proteins able to bind to preselected sites disclosed inco-owned U.S. Pat. No. 6,453,242; WO 00/41566 and PCT/US01/43568. Thetarget site and the amino acid sequences of the recognition regions ofthe zinc fingers of this protein are given in Table 5.

TABLE 5  Designed zinc finger protein binding domains binding  F1  F2 F3  ZFP# target site sequence* sequence* sequence* 1135 HOXB4 GYGGYGGGGGRSDHLAR RSDELQR RSDERKR (SEQ ID  (SEQ ID (SEQ ID (SEQ ID NO: 20) NO: 21)NO: 22) NO: 23) *The amino acid sequences shown are those of amino acids−1 through +6 (with respect to the start of the alpha-helical portion ofthe zinc finger) and are given in the one-letter code

Sequences encoding the ZFP binding domains shown in Table 5 were used togenerate constructs which encode the ZFP fused to a VP16 transcriptionalactivation domain (v-1135) or a p65 transcriptional activation domain(s-1135), using methods disclosed in co-owned U.S. Pat. No. 6,453,242and co-owned WO 00/41566. These constructs were separately transfectedinto mouse ES cells, and their effects on expression of the HOXB4 genewere determined.

Example 6: Regulation of the HOXB4 Gene in Mouse Embryonic Stem CellsUsing an Engineered Zinc Finger Protein

Mouse embryonic stem cells were obtained, propagated and transfected asdescribed in Example 3. Cells were transfected with v-1135 (Example 5),s-1135 (Example 5), or a green-fluorescent protein-encoding vector(GFP).

At 48 h after transfection, total cellular RNA was isolated and analyzedfor HOXB4 mRNA as described in Example 3. Primers and probes used formRNA analysis are given in Table 4.

The results, shown in FIG. 6, indicate that HOXB4 mRNA levels areincreased 2- to 2.5-fold in cells transfected with vectors encoding aHOXB4-targeted ZFP fused to either of the two transcriptional activationdomains. This provides further evidence that key developmental controlgene can be regulated by engineered ZFPs in stem cells.

Example 7: Proliferation and Expansion of Hematopoietic Cells

Hematopoietic stem cells are obtained using, for example, the methodsdescribed in U.S. Pat. No. 5,681,559. Stem cells are cultured in media.ZFP proteins are engineered to target growth factors or other genesinvolved in self-renewal. The ZFPs are administered to cultured stemcells either as proteins or nucleotides encoding same.

To expand B-lymphocyte stem cells, ZFPs that repress expression of E2A,EBF and Pax-5 are administered. Similarly to expand hematopoieticlineages other than B-lymphocytes, ZFPs that repress genes encodingSCL/Tal-1, AML-1 and/or c-Myb are administered to the cell. T-cellprogenitor populations are expanded by administering ZFPs that repressexpression of TCF-1.

Example 8: Use of ZFPs to Differentiate Stem Cells

A. Pancreatic Stem Cell to Liver Cells

Pancreatic stem cells are obtained and cultured as described in Example7 or using methods described in the art. ZFPs that modulate expressionof albumin, b-integrin and other molecules are introduced into thecultured stem cells. Additionally, ZFPs used to maintain the stem cellphenotype in culture are eliminated. The pancreatic stem cells areinduced to a differentiated hepatocyte phenotype characterized byfunctional albumin.

B. Neural Stem Cells into Hematopoietic Cells

Neural stem cells are obtained and cultured as described in Example 7 orby methods known in the art. ZFPs that modulate (e.g., activate)expression of SCL/Tal-1 and/or TCF/liver inhibitory factor (lif) areadministered to the cells, either as proteins or polynucleotidesencoding these ZFPs.

1. An isolated stem cell comprising a human leukocyte antigen (HLA)class I gene, wherein expression of the HLA is repressed by a fusionprotein comprising a DNA binding domain and a repression domain, whereinthe DNA binding domain binds to a target site in the HLA gene.
 2. Theisolated stem cell of claim 1, wherein the HLA gene is a common βsubunit gene.
 3. The isolated stem cell of claim 2, wherein the common βsubunit gene is a β2 microglobulin gene.
 4. The isolated stem cell ofclaim 1, wherein the repression domain is a transcriptional repressiondomain.
 5. The isolated stem cell of claim 1, wherein the repressiondomain comprises an endonuclease that cleaves the HLA gene.
 6. A methodof generating a stem cell according to claim 1, the method comprising:introducing a polynucleotide encoding the fusion protein into the stemcell such that the fusion protein is expressed and HLA expression isrepressed.
 7. The method of claim 6, wherein the HLA gene is a common βsubunit gene.
 8. The method of claim 7, wherein the common β subunitgene is a β2 microglobulin gene.
 9. The method of claim 6, wherein therepression domain is a transcriptional repression domain.
 10. The methodof claim 6, wherein the repression domain comprises an endonuclease thatcleaves the HLA gene.
 11. An isolated HLA class I null stem cellgenerated by the method of claim
 6. 12. A method of providing anallogenic stem cell graft to a subject in need thereof, the methodcomprising providing the subject with an isolated stem cell according toclaim
 1. 13. The method of claim 9, wherein the subject's immuneresponse to the graft is reduced as compared to stem cells in which HLAis not repressed.